System for suppressing one-sided movement and zigzag running of a conveyor belt in an image forming apparatus

ABSTRACT

An image forming apparatus includes an image former for forming an image on an image carrier, a conveyor belt for conveying an image receiving medium to the image carrier, a conveyor roller structure having a first roller with different diameter at both ends and taper size T expressed by T=(D-d)/L, wherein D is the diameter at the large diameter side, d is the diameter at the small diameter side and L is the length of the first roller, which is more than 2.341×10 -3  and a coefficient of static friction is less than 0.26. A second roller is provided opposite to the first roller, for moving the conveyor belt in a prescribed direction by rotating the first and the second rollers in a state where the conveyor belt is put over the first and the second rollers, and a transferring structure for transferring the image formed on the image carrier onto the image receiving medium.

This application is a continuation-in-part of application Ser. No.08/205,851, filed Mar. 4, 1994, now U.S. Pat. No. 5,481,338.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to image forming apparatus which formimages on an image receiving medium using a plurality of photosensitivedrums such as a color copying machine, etc.

2. Description of the Related Art

There is a color copying machine comprising four photosensitive drumsarranged in parallel. In this type of copying machine, fourphotosensitive drums are arranged and toner images in different colorsare formed on the respective photosensitive drums using yellow, magenta,cyanic and black toners. Each of these toner images is transferred andformed on a single sheet of paper.

In the color copying machine using these four photosensitive drums, animage receiving medium placed on a conveyor belt is brought in contactwith the four photosensitive drums one by one and respective tonerimages are transferred from the drums onto the image receiving medium.

Further, when forming an image other than color images, for instance,forming a black image only, no toner image is formed on the yellow,magenta and cyanic drums and a black toner image is formed andtransferred onto an image receiving medium. Thus, an image only in blackis obtained.

However, a conveyor belt is normally wound around driving rollerscomprising rubber rollers and is moved by rotating the driving rollers.The largest reason for using rubber rollers is to prevent the conveyorbelt from slipping against the driving rollers by making the coefficientof statical friction of the rubber rollers with the conveyor belt large.

Because, if the conveyor belt slips against the driving rollers, themoving distances of copying papers being conveyed by the conveyor beltchanges, causing a color shift on the image receiving medium in theconveying direction. That is, in order to prevent the conveyor belt fromslipping against the driving rollers, it is desirable to use soft rubberrollers with hardness of rubber lowered.

However, if a rubber roller is used, accuracy of the outer diameter ofthe driving roller drops and the softer a rubber roller is, the worsethe accuracy of the outer diameter of the driving roller will become. Ifaccuracy of the outer diameter of the driving roller drops, theperipheral speed of the roller changes, making the conveying speed ofthe conveyor belt irregular and finally, a color shift is caused oncopying papers in the conveying direction.

When a conveyor belt is used for a long time, its surface becomes dirtyas toners and paper powder of the image receiving medium attach thereonand therefore, the conveyor belt is cleaned with a belt cleaning device.However, this conveyor belt cleaning device cleans a belt by bringing arubber blade in contact with the surface of the conveyor belt and amaterial having a high contact resistance against a rubber blade is usedas the conveyor belt. Therefore, when a conveyor belt is rubbed by arubber blade of a belt cleaning device which is kept in contact with theconveyor belt, electric charge is left. Unless this residual electriccharge is neutralized, the residual potential of the conveyor beltbecomes high and images are not satisfactorily transferred on the imagereceiving medium. Furthermore, a problem is also caused that ozone isgenerated if a corona discharger is used to neutralize the residualelectric charge.

In this type of image forming apparatus, there was a problem that theconveying speed of a conveyor belt becomes irregular as its peripheralspeed changes if the accuracy of the outer diameter of driving rollersdrop and as a result, a color shift of images on an image receivingmedium may be caused along the conveying direction of the imagereceiving medium.

Further, as described above, the image receiving medium is conveyedtoward four photosensitive drums by a conveyor belt. However, if theconveyor belt is moved while meandering unwillingly, the image receivingmedium is also conveyed while meandering correspondingly and there was aproblem that the same images in different colors will be shifted as theimages in different colors are transferred sequentially on the imagereceiving medium as a result of the meandering conveyance.

In order to solve This problem, a regulation plate is provided at bothends of the rollers over which a conveyor belt is put as disclosed inthe Japanese Utility Model Laid-open Publication (JITSU-KAI-HEI) 4-7543.The conveyor belt is moved while keeping its both ends in contact withthese regulation plates to prevent the conveyor belt from meandering.

In this construction, however, if a distance between two regulationplates provided at the rollers is not in accord with the width of aconveyor belt, a problem described below will be caused. That is, therewill be a problem that at a place where the distance between two controlplates is wide, it is possible for the conveyor belt to meander and at aplace where the distance between two control plates is narrow, theconveyor belt may possibly run over one of the regulation plates and asa result, a color shift will be caused on images on the image receivingmedium along the direction perpendicular to the conveying direction ofthe image receiving medium.

Further, in a conventional image forming apparatus, the rollers arerotated by transmitting the turning force of a motor to one of therollers having parallel shafts over which a conveyor belt is put and aconveying force is provided by moving the conveyor belt in the rotatingdirection of the rollers. There was a problem that if the moving speedof the conveyor belt becomes irregular, it is not possible to transferimages from four photosensitive drums at a prescribed position and as aresult, a color shift is caused on images on the image receiving medium.In view of this problem, construction to use driving rollers directly asthe rotary shaft of a motor without using driving transmission gears,etc. which may cause irregular moving speed of a conveyor belt. That is,a driving roller and a motor are in one united body. There are a beltcleaner, photosensitive drums, image transfer rollers, etc. arrangedwhile kept in contact with this conveyor belt along its surface. Thesearrangements, however, will become loads when driving the conveyor belt.Further, when processing jammed image receiving medium, the conveyorbelt is separated from the state in contact with the photosensitivedrums and pulled out of the body of the apparatus. Because of thisconstruction, in order to pull out the conveyor belt easily it isnecessary to lower the belt to a location where the motor does not comein contact with the photosensitive drums.

On the other hand, in order to drive a conveyor belt while overcomingloads, a motor needs a large torque. Generally, a motor large in size isused to improve its torque. However, because a roller and a motor fordriving the conveyor belt are in one united body as described above, ifa large motor is used, it becomes necessary to further lower theconveyor belt to prevent the photosensitive drums and the motor fromcontacting each other when processing jammed image receiving medium.Thus, there comes out a problem that the entire image forming apparatuswill become large in size.

SUMMARY OF THE INVENTION

It is one of the objects of the present invention to provide an imageforming apparatus which does not cause a color shift of images along theconveying direction of an image receiving medium.

Another object of the present invention is to provide an image formingapparatus which does not become large in size even when a motorgenerating a large torque is used for driving rollers over which aconveyor belt is put.

A further object of the present invention is to provide an image formingapparatus which does not cause a color shift of images along thedirection perpendicular to the conveying direction of an image receivingmedium.

According to the present invention, there is provided an image formingapparatus comprising means for forming images on a plurality of imagecarriers, a conveyor belt for carrying an image receiving medium, adriving roller on which the conveyor belt is mounted for driving theconveyor belt to convey the image receiving medium, a pressing rollerfor pressing the conveyor belt against the driving roller, and means fortransferring the images from the image carriers to the image receivingmedium conveyed by the conveyor belt.

Further, according to the present invention, there is provided an imageforming apparatus comprising means for forming images on a plurality ofimage carriers, a conveyor belt for carrying an image receiving medium,a plurality of rollers on which the conveyor belt is mounted for movingthe conveyor belt to convey the image receiving medium sequentially tothe image carriers, an outer rotor type motor having a rotated outerhousing provided to one of the rollers for driving the conveyor belt tomove the conveyor belt by a friction of the rotated outer housing withthe conveyor belt, and means for transferring the images from the imagecarriers to the image receiving medium conveyed by the conveyor belt.

Yet further, according to the present invention, there is provided animage forming apparatus comprising means for forming images on aplurality of image carriers; a conveyor belt having a first peripheraledge and a second peripheral edge opposing to the first peripheral edgefor carrying an image receiving medium, the conveyor belt having a firstlength L1 at the first periperal edge and a second length L2 at thesecond peripheral edge shorter than the first length L1; a plurality ofrollers on which the conveyor belt is mounted for moving the conveyorbelt to convey the image receiving medium sequentially to the imagecarriers; a tensioning means for giving a tension to the conveyor beltso as to skid the conveyor belt toward the second peripheral edge whenthe conveyor belt is moved by the rollers; a regulation member forregulating the skid of the conveyor belt; and means for transferring theimages from the image carriers to the image receiving medium conveyed bythe conveyor belt.

Still further, according to the present invnetion, there is provided animage forming apparatus comprising means for forming images on aplurality of image carriers, a conveyor belt for carrying an imagereceiving medium, a plurality of rollers on which the conveyor belt ismounted for moving the conveyor belt to convey the image receivingmedium sequentially to the image carriers, the rollers including atleast one tensioning roller having a contact surface non-parallel to aremaining roller for giving a tension to the conveyor belt so as to skidthe conveyor belt toward one end of the rollers when the conveyor beltis moved, a regulation member for regulating the skid of the conveyorbelt, and means for transferring the images from the image carriers tothe image receiving medium conveyed by the conveyor belt.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an outline diagram of full color image forming apparatusaccording to the present invention applied;

FIG. 2 is a perspective view of a conveying means using a pinch rollershowing the first embodiment of the present invention;

FIG. 3 is a front view of the conveying means using the pinch rollershown in FIG. 2:

FIG. 4 is a perspective view of the conveying means using the pinchroller showing the second embodiment of the present invention;

FIG. 5 is a front view of the conveying means using the pinch rollershown in FIG. 4;

FIG. 6 is a perspective view of the conveying means using a windingroller showing the third embodiment of the present invention;

FIG. 7 is a front view of the conveying means using the winding rollershown in FIG. 6;

FIG. 8 is a perspective view of the conveying means using a windingroller showing the fourth embodiment of the present invention;

FIG. 9 is a front view of the conveying means using the winding rollershown in FIG. 8;

FIG. 10 is a perspective view of the conveying means with a dischargingroller provided showing the fifth embodiment of the present invention;

FIG. 11 is a prespective view of the conveying means with thedischarging roller shown in FIG. 10 provided as the pinch roller shownin the first embodiment;

FIG. 12 is a perspective view showing the sixth embodiment of thepresent invention less a part of the conveying means which is itsessential part;

FIG. 13 is a graph showing a test result of difference in peripherallengths and amount of skid movement of the conveyor belt;

FIG. 14 is a graph showing a test result of weighing and skid amount ofthe conveyor belt;

FIG. 15A through 15C are cross-sectional views showing the positionalrelation between the conveyor belt and the regulation belt;

FIG. 16 is a graph showing the state of skid movement of the conveyorbelt when the construction of the sixth embodiment is not adopted;

FIG. 17 is a graph showing the state of skid movement of the conveyorbelt when the construction of the sixth embodiment is adopted;

FIG. 18 is a perspective view showing the seventh embodiment of thepresent invention less a part of the conveying means which is itsessential part;

FIG. 19 is a plan view of the seventh embodiment less a part of theconveying means;

FIG. 20 is a perspective view for explaining the skid movement of theconveyor belt in the seventh embodiment;

FIG. 21 is a front view for explaining the size and tapered state of atapered roller used in the seventh embodiment;

FIG. 22 is a graph showing the state of skid movement of the conveyorbelt when the construction of the seventh embodiment is not adopted;

FIG. 23 is a graph showing the state of skid movement of the conveyorbelt when the construction of the seventh embodiment is adopted;

FIG. 24 is a perspective view showing the eighth embodiment less a partof the conveying means which is its essential part.

FIG. 25 is a plan view showing the eighth embodiment less a part of theconveying means;

FIG. 26 is a perspective view for explaining the skid movement of theconveyor belt in the eighth embodiment;

FIG. 27 is a graph showing the state of skid movement of the conveyorbelt when the construction of the eighth embodiment is not adopted;

FIG. 28 is a graph showing the state of skid movement of the conveyorbelt when the construction of the eighth embodiment is adopted;

FIG. 29 is a perspective view showing the ninth embodiment of thepresent invention less a part of the conveying means which is itsessential part;

FIGS. 30A through 30C are cross-sectional views showing the positionalrelation of the conveyor belt and the regulation plate;

FIG. 31 is a graph showing the state of skid movement of the conveyorbelt when the construction of the ninth embodiment is not adopted;

FIG. 32 is a graph showing the state of skid movement of the conveyorbelt when the construction of the ninth embodiment is adopted;

FIG. 33 is a perspective view showing the tenth embodiment of thepresent invention less a part of the conveying means which is itsessential part;

FIG. 34 is a perspective view showing the eleventh embodiment of thepresent invention less a part of the conveying means which is itsessential part;

FIG. 35 is a perspective view showing the twelfth embodiment of thepresent invention less a part of the conveying means which is itsessential part;

FIG. 36 is a perspective view for explaining the skid movement of theconveyor belt in the twelfth embodiment;

FIG. 37 is a graph showing the state of skid movement of the conveyorbelt when the construction of the twelfth embodiment is not adopted;

FIG. 38 is a graph showing the state of skid movement of the conveyorbelt when the construction of the twelfth embodiment is adopted;

FIG. 39 is a perspective view showing the thirteenth embodiment less apart of the conveying means which is its essential part;

FIG. 40 is a perspective view for explaining the skid movement of theconveyor belt in the thirteenth embodiment;

FIG. 41 is a graph showing the state of skid movement of the conveyorbelt when the construction of the thirteenth embodiment is not adopted;

FIG. 42 is a graph showing the state of skid movement of the conveyorbelt when the construction of the thirteenth embodiment is adopted;

FIG. 43 is an outline diagram of full-color image forming apparatusshowing the fourteenth embodiment of the present invention;

FIG. 44 is a perspective view showing the construction of the conveyorbelt unit of the full-color image forming apparatus shown in FIG. 43;

FIG. 45 is an outline diagram showing the state of the conveyor beltunit separated from the photosensitive drums shown in FIG. 44;

FIG. 46 is an explanatory diagram showing Fleming's left hand rule;

FIG. 47 is an explanatory diagram showing the principle of operation ofa DC motor;

FIG. 48 is a diagram showing the principal construction of a steppingmotor;

FIG. 49 is an explanatory diagram showing the principle of operation ofthe stepping motor shown in FIG. 48; and

FIG. 50 is a block diagram for controlling the roller in-motor which isused in the conveyor belt unit shown in FIG. 44.

FIG. 51 is a perspective view showing a one-sided moving force measuringunit for measuring a one-sided moving force of a conveyor belt which isused on the image forming apparatus shown in FIG. 1;

FIG. 52 is a diagram showing the results of the test which investigatedthe effects of taper sizes and coefficients of static friction of aconveyor belt with a load of 2.5 kg applied on the one-sided movingforce of the conveyor belt using the one-sided moving force measuringunit as shown in FIG. 51;

FIG. 53 is a diagram showing the results of the test which investigatedthe effects of taper sizes and coefficients of static friction of aconveyor belt with a load of 2.75 kg applied on the one-sided movingforce of the conveyor belt using the one-sided force measuring unitshown in FIG. 51;

FIG. 54 is a diagram showing the results of the test which investigatedthe effects of taper sizes and coefficients of static friction of aconveyor belt with a load of 3.0 kg applied on the one-sided movingforce of the conveyor belt using the one-sided force measuring unitshown in FIG. 51;

FIG. 55 is a diagram showing the results of the test which investigatedthe effects of taper sizes and coefficients of static friction of aconveyor belt with a load of 3.25 kg applied on the one-sided movingforce of the conveyor belt using the one-sided force measuring unitshown in FIG. 51;

FIG. 56 is a diagram showing the results of the test which investigatedthe effects of taper sizes and coefficients of static friction of aconveyor belt with a load of 3.5 kg applied on the one-sided movingforce of the conveyor belt using the one-sided force measuring unitshown in FIG. 51;

FIG. 57 is a perspective view showing an apparatus used in a testaccording to the TAGUCHI Method, which is an embodiment of the presentinvention;

FIG. 58 is a diagram showing the effects of factors in the results ofthe tests (S/N ratio) using the apparatus shown in FIG. 57;

FIG. 59 is a perspective view showing a regulation plate type conveyorbelt conveying apparatus, which is an embodiment of the presentinvention;

FIG. 60 is a diagram showing the one-sided and zigzag moving volume whenthe regulation plate shown in FIG. 59 was used;

FIG. 61 is a perspective view showing the regulation belt type conveyorbelt conveying apparatus which is another embodiment of the presentinvention;

FIG. 62 is a diagram showing the one-sided and zigzag moving volume whenthe regulation belt type conveyor belt conveying apparatus shown in FIG.61;

FIG. 63A is a front view showing the state of the driving roller and thedriven roller of the belt conveying apparatus shown in FIG. 61; and

FIG. 63B is a side view showing the state of the driving roller and thedriven roller of the belt conveying apparatus shown in FIG. 61.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the preferred embodiments of the present invention will bedescribed in detail with reference to the drawings.

A first embodiment will be described with reference to FIGS. 1 through3.

FIG. 1 shows the outline of the construction of a color copying machineas an image forming apparatus. In this color copying machine, fourphotosensitive drums 2Y, 2M, 2C and 2BK are arranged in parallel in thisorder as image carriers. Above these photosensitive drums, there arefour image forming units 150Y, 150M, 150C and 150BK providedcorrespondingly for forming images on the respective photosensitivedrums. Under these photosensitive drums there is a conveying means 200provided for conveying an image receiving medium 8, e.g. a sheet ofpaper, to the photosensitive drums 2Y, 2M, 2C and 2BK. Transfer rollers5Y, 5M, 5C and 5BK are arranged corresponding to the photosensitivedrums 2Y, 2M, 2C and 2BK as image transfer means for transferring tonerimages formed on the photosensitive drums onto image receiving medium 8conveyed by the conveying means 200.

Four sets of the image forming units 150Y, 150M, 150C and 150BK arecomposed of a recording unit comprising charging devices 3Y, 3M, 3C and3BK, solid scanning heads 1Y, 1M, 1C and 1BK, developing devices 4Y, 4M,4C and 4BK, cleaning devices 6Y, 6M, 6C and 6BK and discharging devices7Y, 7M, 7C and 7BK respectively.

Now, a yellow image forming unit 150Y will be described. The solidscanning head 1Y outputs exposure light to the photosensitive drum 2Yaccording to yellow image data being sent from a printing controller(not shown). The solid scanning head 1Y is in such a construction thatit has very small light emitting sections arranged at equal spaces inthe direction of the axis of rotation of the photosensitive drum 2Y,that is, on the line in the main scanning direction.

Lighting of the individual light emitting sections on the line of themain scanning direction is controlled according to the on-off signalssent from a printing controller according to a pattern to be printed. Alight image is exposed on the photosensitive drum 2Y corresponding to anoriginal image from the light emitting sections on one for one basis. AnLED head array of resolution 400 DPI was used for the solid scanninghead 1Y.

The charging device 3Y which charges the surface of the photosensitivedrum 2Y, the developer device 4Y, the transfer device 5Y, the cleaningdevice 6Y and the discharging device 7Y are sequentially arranged aroundthe photosensitive drum 2Y.

The photosensitive drum 2Y is rotated and driven by a driving motor (notshown). The surface of the photosensitive drum 2Y is charged by thecharging device 3Y which is composed of a conductive charging roller andprovided in contact with the surface of the photosensitive drum 2Y.Further, the charging roller is rotating when kept in contact with thesurface of the photosensitive drum 2Y.

The surface of the photosensitive drum 2Y is formed by an organicphotoconductor. Normally, this photoconductor has a high resistance buthas a nature to change specific resistance of a lighted portion whenlight is applied. When light is applied to the charged surface of thephotosensitive drum 2Y from the solid scanning head 1Y corresponding toa yellow print pattern, an electrostatic latent image of the yellowimage pattern is formed on the surface of the photosensitive drum 2Y.

The electrostatic latent image is a so-called negative latent image thatis formed on the surface of the photosensitive drum 2Y through chargingwhen specific resistance of the lighted surface of a photoconductor isdropped by the light applied from the solid scanning head 1Y todischarge electric charge on the surface of the photosensitive drum 2Yand on the other hand, electric charge of the portion to which no lightwas applied remains.

Thus, the light from the solid scanning head 1Y forms an image at anexposing positional location on the charged photosensitive drum 2Y andthe photosensitive drum 2Y with a latent image formed rotates to adeveloping position. Then, the latent image on the photosensitive drum2Y is turned to a toner image as a visible image, by the developingdevice 4Y.

The developing device 4Y contains a yellow toner containing a yellow dyeformed of resin. This yellow toner is frictionally charged when stirredin the developing device 4Y and has an electric charge of the samepolarity as that charged on the photosensitive drum 2Y. When the surfaceof the photosensitive drum 2Y passes through the developing device 4Y,the yellow toner is adhered electrostatically to the discharged latentimage portion only and this latent image is developed by the yellowtoner.

The photosensitive drum 2Y with the yellow toner image formed on it isrotating continuously and the yellow toner image is transferred onto theimage receiving medium 8 on the conveyor belt 12, that is timely fed bythe transfer device 5Y which is in the transfer position. The conveyorbelt 12 is mounted on driving roller 16 and the driven roller 17. Thedriven roller 17 is held by the driven roller holder 21.

A paper supply means is composed of a pickup roller 9, a feed roller 10and a register roller 11. The image receiving medium 8 taken out of apaper supply cassette 23 by the pickup roller 9 is conveyed to theregister roller 11 by one sheet only by the feed roller 10. The registerroller 11 feeds the image receiving medium 8 after properly correctingits position. The peripheral velocity of the register roller 11 and thatof the conveyor belt 12 have been so set that they become equal to theperipheral velocity VO of the photosensitive drum 2Y. The imagereceiving medium 8 is conveyed to the transfer position of thephotosensitive drum 2Y together with the conveyor belt 12 at apredetermined velocity equal to that of the photosensitive drum 2Y whilebeing partially kept by the resister roller 11.

The yellow toner image on the photosensitive drum 2Y which is kept incontact with the image receiving medium 8 is removed from thephotosensitive drum 2Y and transferred onto the image receiving medium 8by the transfer device 5Y. As a result, the yellow toner image in aprint pattern based on a yellow print signal is formed on the imagereceiving medium 8.

The transfer device 5Y is composed of a semiconductive transfer roller.This transfer roller 5Y supplies an electric field having the polarityreverse to a potential of the yellow toner adhered statically to thephotosensitive drum 2Y through the back side of the conveyor belt 12.This electric field acts on the yellow toner image on the photosensitivedrum 2Y through the image receiving medium 8 and as a result, the yellowtoner image is transferred onto the image receiving medium 8 from thephotosensitive drum 2Y.

The image receiving medium 8 with the yellow toner image thustransferred is conveyed sequentially to a magenta image forming unit150M, a cyanic image forming unit 150C and further to a black imageforming unit 150BK.

Further, the magenta image forming unit 150M, the cyanic image formingunit 150C and the black image forming unit 150BK contain a magenta (M),cyanic (C) and black (BK) color developers, respectively, instead of ayellow (Y) developer contained in a developing device 4Y for the yellowimage forming unit 150Y. As these image forming units are constructedfrom the same components and their operations are all the same, theexplanations of these image forming units will be omitted to make theexplanation simple.

Now, the image receiving medium 8 with color images formed one overanother while passing through the yellow, magenta, cyanic and blacktransfer positions is conveyed to a fixing device 13.

The fixing device 13 is composed of a heat roller with a heaterincorporated therein which fixes the toner images in various colors onthe image receiving medium 8 permanently by heating and fusing the colortoners. The image receiving medium 8 with the fixed image is ejected ona receiving tray 15 by the exit roller 14.

On the other hand, the photosensitive drums 2Y, 2C and 2BK in respectivecolors passed through the transfer positions are driven and cleaned bycleaning devices 6Y, 6M, 6C and 6BK to remove residual toners and paperpowder on the drums. Further, the potentials on the surfaces of thephotosensitive drums 2Y, 2M, 2C and 2BK are regulated to a certainlevel. Then, a series of image forming processes from the chargingdevices 3Y, 3M, 3C and 3BK will begin.

After conveying the image receiving medium 8 to the fixing device 13,the conveyor belt 12 is cleaned by a cleaning device 22 to removeresidual toners and paper powder adhered to the surface of the belt andconveys the next image receiving medium 8 when required.

Further, in the case of a unicolor print, the image forming by an imageforming unit in a desired unicolor is carried out. At this time, otherimage forming units in colors other than the selected color do notperform their operations.

Next, a conveying means 200₁ in the first embodiment will be explainedwith reference to FIGS. 2 and 3.

The conveying means 200₁ is composed of an endless conveyor belt 12₁which is put and extended over a parallelly provided driving roller 16₁and a driven roller 17₁ with the middle section stretched opposing tothe photosensitive drums 2Y, 2M, 2C and 2BK.

The driven roller 17₁ is pressed by a compression spring 18 (see FIG.1), giving a tensile force to the conveyor belt 12₁.

The conveyor belt 12₁ is an endless type and is retained by the drivingroller 16₁ at the fixing device 13 side and the driven roller 17₁ at theimage receiving medium supply side. The driving roller 16₁ is given itsdriving force from a driving motor (not shown) and is driven so that aprescribed peripheral velocity of the photosensitive drum becomes equalto that of the belt.

On the other hand, the driven roller 17₁ has a mechanism at both sidesof the roller, which makes the roller movable in the direction parallelto the image receiving medium conveying direction. That is, the drivenroller 17₁ is pressed in the direction opposite to the image receivingmedium conveying direction by the compression spring 18 to give atensile force to the conveyor belt 12₁. The mechanism of the drivenroller 17₁ which makes it possible to move in the direction parallel tothe image receiving medium conveying direction is composed of a slot(not shown) provided on the frame and a driven roller holder (not shown)which slides in the slot and makes the driven roller 17₁ rotatable.

The driving roller 16₁ uses a roller with urethane rubber having aradial thickness of 1 mm baked to a metallic roller. The reason forusing rubber on the surface is to prevent the conveyor belt 12₁ fromslipping on the driving roller 16₁. As described above, the imagereceiving medium 8 is conveyed to four photosensitive drums 2Y, 2M, 2Cand 2BK by the conveyor belt 12₁ and images on the respective drums aretransferred onto the image receiving medium 8. As the image receivingmedium 8 is moved by the same distance as the conveyor belt 12₁, if aslip is caused between the conveyor belt 12₁ and the driving roller 16₁,the image receiving medium 8 is forced to stay in a delayed positionfrom a position where it is originally to be. This will cause the colorshift on the images transferred one over another on the image receivingmedium 8.

The use of the rubber type driving roller 16₁ increases a coefficient ofstatic friction with the conveyor belt 12₁. To further increase itsreliability, it is only necessary to increase the static frictioncoefficient. That is, it is needed to make the rubber soft and increaseits thickness.

Further, it is needed to increase a contact pressure to the drivingroller 16₁ by increasing a tensile force of the conveyor belt 12₁.However, when the rubber is made soft and its thickness is increased,manufacturing accuracy of the roller drops. As described previously, theimage receiving medium 8 is conveyed by the conveyor belt 12₁. Ifaccuracy of the outer diameter of the driving roller 16₁ is bad, adifference will be caused in the peripheral velocity of the conveyorbelt 12₁ and that of the peripheral surface of the driving roller 16₁according to which the belt is moved.

That is, coarse accuracy of the outer diameter of the driving roller 16₁means that a radial size at a first position in the axial direction ofthe driving roller 16₁ is different from that at a second position. Thedriving roller 16₁ is rotated by a driving force transmitted through itsshaft and the rotating peripheral velocity differs at the first andsecond positions of which radial sizes differ from each other. Theconveying velocity of the conveyor belt 12₁ which is wound around thefirst position is also different from that of the second position. Adifference in these conveying velocities causes the color shift of thetransferred images.

Therefore, a roller which has the accurate outer diameter and a largecoefficient of static friction with the conveyor belt 12₁ is desirableas a driving roller. Generally, a rubber roller is inferior to ametallic roller when viewed from accuracy of the outer diameter. On theother hand, when viewed from coefficient of static friction, a rubberroller is superior to a metallic roller.

A metallic roller is used for the driving roller 16₁ and the drivenroller 17₁ uses a metallic roller en which the conveyor belt 12₁ ismounted. A pinch roller 25₁ composed of a rubber roller is pressedagainst the driving roller 16₁ at the fixed position from the outside ofthe conveyor belt 12₁ so that the conveyor belt 12₁ is wound around thedriving roller 16₁ at a winding angle above 180°.

FIG. 2 shows a prospective view of a system using the pinch roller 25₁and FIG. 3 shows its front view. Both ends of the shaft of the pinchroller 25₁ are fixed to a bearing 26₁ in the rotatable state. Thisbearing 26₁ is put into a slot 28₁ of the pinch roller holder 27₁. Thisslot 28₁ is provided in a state where the direction of the drivingroller 16₁ becomes long. Therefore, the pinch roller 25₁ is movable inthe direction to come in contact with/separate from the driving roller16₁ while rotating.

A tension spring 29₁ is hooked on this bearing 26₁ in the direction toapply a pressure to the rotation shaft of the driving roller. A tensionspring 30₁ is hooked on the pinch roller holder 27₁ in the direction tohave the pinch roller 25₁ press the conveyor belt 12₁ inward. Therefore,the pinch roller 25₁ presses the conveyor belt 12₁ against the drivingroller 16₁ and rolls the conveyor belt 12₁ inward. A pressure to pressthe conveyor belt 12₁ against the driving roller 16₁ is set larger thanthe pressure to roll in the conveyor belt 12₁ so that it does not moveaway from the driven roller 17₁ when the pinch roller 25₁ rolls theconveyor belt 12₁ inward.

In this embodiment, a pressure to press the conveyor belt 12₁ againstthe driving roller 16₁ was set at 6 to 7 kg and a pressure to roll inthe conveyor belt 12₁ at 3 to 5 kg. This pressure to roll in theconveyor belt 12₁ directly becomes a tensile force of the conveyor belt.The driving roller 16₁ can be composed of a metallic roller using thepinch roller 25₁ as described above and therefore, the driving roller16₁ of good outer diameter accuracy can be used. Further, when ametallic roller is used as the driving roller 16₁, it is possible todrive the conveyor belt 12₁ by the pinch roller 25₁ without slippingagainst the driving roller 16₁.

Next, the conveying means 200₂ in the second embodiment will bedescribed with reference to FIGS. 4 and 5.

In the second embodiment, a conveying means 200₂ is composed in such aconstruction that metallic rollers are used for driving roller 16₂ anddriven roller 17₂ over which a conveyor belt 12₂ is put and the positionof the driving roller 16₂ only is fixed. A pinch roller 25₂ composed ofa rubber roller is pressed against the driving roller 16₂ from theoutside of the conveyor belt 12₂.

The driven roller 17₂ is provided with a mechanism at the shaft of bothsides of the roller to make the roller movable in the direction parallelto the conveying direction of the image receiving medium 8. That is, thedriven roller 17₂ is pressed by a compression spring 18₂ in thedirection reverse to the conveying direction of the image receivingmedium 8 to apply a tensile load to the conveyor belt 12₂.

The mechanism to make the driven roller 17₂ movable in the directionparallel to the conveying direction of the image receiving medium 8 iscomposed of a slot provided on the frame and a driven roller holder 21₂which is able to slide in the slot and holds the driven roller 17₂ in arotatable state.

FIG. 4 shows a perspective view of a system using a pinch roller andFIG. 5 shows its front view. Both ends of the shaft of the pinch roller25₂ are fixed to a bearing 26₂ in the rotatable state. This bearing 26₂is fitted into a slot 32₂ of a belt frame 31₂. This slot 32₂ is providedin a state where the direction of the driving roller 16₂ becomes long.Therefore, the pinch roller 25₂ is movable in the direction to come incontact with/separate from the driving roller 16₂ while rotating.

A tension spring 29₂ (see FIG. 5) is hooked on this bearing 26₂ in thedirection to apply a pressure to the driving roller 16₂. Therefore, thepinch roller 25₂ presses the conveyor belt 12₂ against the drivingroller 16₂.

In the second embodiment, a pressure to press the conveyor belt 12₂against the driving roller 16₂ was set at 6 to 7 kg and a force to applytensile load to the conveyor belt 12₂ by the compression spring 18₂ wasset at 3 to 5 kg. As a metallic roller can be used for the drivingroller 16₂, a driving roller in good outer diameter accuracy can beused. Further, even when a metallic roller is used for the drivingroller 16₂, it is possible to move the conveyor belt 12₂ by the pinchroller 25₂ without slipping against the driving roller 16₂.

As described above, use of the pinch roller 25₂ in a simple constructionmakes it possible to prevent the conveyor belt 12₂ from slipping againstthe driving roller 16₂ and eliminate an image color shift on the imagereceiving medium in the conveying direction due to the slip of theconveyor belt.

Next, a conveying means 200₃ in the third embodiment will be describedwith reference to FIGS. 6 and 7.

In the third embodiment, a metallic roller is used for a driving roller16₃ and a driven roller 17₃ on which a conveyor belt 12₃ is put. Theserollers 16₃ and 17₃ are fixed and a winding roller 33₃, which is arubber roller, is arranged while pressing it from the outside of theconveyor belt 12₃. The winding angle of the conveyor belt to the drivingroller is set at below 180°.

FIGS. 6 shows a perspective view of a system using the winding roller33₃ and FIG. 7 shows its front view. Reference number 34₃ shows a pairof winding roller bearings, 35₃ shows a pair of winding roller holdersand 36₃ shows holes provided on the winding roller holders 35₃. Therotary shafts at both sides of the winding roller 33₃ are fixed to thebearings 34₃ in a rotatable state. The bearings 34₃ are fitted in theholes 36₃ of the winding roller holders 35₃, respectively.

These holes 36₃ are provided at positions parallel to the shaft of thedriving roller 16₃. Each or the winding roller holders 35₃ is providedwith a tensile spring 30₃ which gives a tensile force to the conveyorbelt 12₃ by pressing the winding roller 33₃ against the inside of theconveyor belt 12₃. Therefore, the winding roller 33₃ is able to bringthe conveyor belt 12₃ in contact with the driving roller 16₃ at awinding angle above 180°. A tensile force to be generated on theconveyor belt 12₃ when the winding roller 33₃ rolls the conveyor belt12₃ in was so set that it becomes 3 to 5 kg.

Next a conveying means 200₄ in the fourth embodiment will be describedwith reference to FIGS. 8 and 9.

In the fourth embodiment, a metallic roller is used for a driving roller16₄ and a driven roller 17₄ over which a conveyor belt 12₄ is put, andonly the position of the driving roller 16₄ is fixed. A winding roller33₄ which is a rubber roller, is fixed to press the conveyor belt 12₄from its outside at the center of the driving roller 16₄ and the drivenroller 17₄.

The driven roller 17₄ is provided with a mechanism which makes itmovable in the direction parallel to the conveying direction of theimage receiving medium 8 at the shaft at both sides of the roller. Thatis, the driven roller 17₄ is pressed by a compression spring 18₄ in thedirection reverse to the conveying direction of the image receivingmedium 8 to apply a tensile load to the conveyor belt 12₄.

The mechanism to make the driven roller 17₄ movable in the directionparallel to the conveying direction of the image receiving medium 8 iscomposed of slot 32₄ provided on the frame 31₄ and a driven rollerholder 21₄ which is able to slide in the slot 32₄ and holds the drivenroller 17₄ in the rotatable state.

FIG. 8 shows a perspective view of a system using a winding roller 33₄and FIG. 9 shows its front view. Reference number 34₄ shows a bearing ofthe winding roller 33₄ and 31₄, shows a belt frame. Both ends of theshaft of the winding roller 33₄ are fixed to bearings 34₄ in a rotatablestate. The bearing 34₄ is fitted in a hole provided on the belt frame31₄. This hole is provided at a position where the winding roller 33₄presses the conveyor belt 12₄ against the inside and it is parallel tothe driving roller 16₄. Therefore, the winding roller 33₄ is able tobring the conveyor belt 12₄ in contact with the driving roller 16₄ at awinding angle above 180°.

In this fourth embodiment, the compression spring 18₄ is compressed asthe conveyor belt 12₄ is pressed inward by the winding roller 33₄ togive a tensile load of 3 to 5 kg to the conveyor belt 12₄.

As a metallic roller can be used for the driving roller 16₄ when thewinding roller 33₄ is used as described above, it becomes possible touse the driving roller 16₄ in good outer diameter accuracy. Further,even when a metallic roller is used for the driving roller 16₄, a largecontact area between the driving roller 16₄ and the conveyor belt 12₄can be made available by the winding roller 33₄ and therefore, it ispossible to drive the conveyor belt 12₄ without slipping against thedriving roller 16₄.

As described in detail in the above, use of the winding roller 33₄ invery simple construction makes it possible to hove the conveyor belt 12₄at a constant velocity without slipping between the conveyor belt 12₄and the driving roller 16₄. Accordingly, it is also possible toeliminate the color shift on the formed images transferred on the imagereceiving medium 8 in the conveying direction of the conveyor belt 12₄.

Next, a conveying means 200₅ in the fifth embodiment will be describedwith reference to FIGS. 10 and 11.

FIG. 10 shows a perspective view of a system using a discharging roller37₅. Reference number 38₅ is an AC power supply unit and 39₅ is acontroller. A driving roller 16₅ is composed of a metallic roller with aconductive rubber wound around it and therefore it is conductive. Thedriving roller 16₅ is electrically earthed. A conveyor belt 12₅ is woundaround the driving roller 16₅ and a conductive metallic dischargingroller 37₅ is provided in contact with the conveyor belt 12₅.

The discharging roller 37₅ is arranged in contact with the conveyor belt12₅. In this embodiment, the metallic discharging roller 37₅ is used butis not limited to a roller if it is conductive. For instance, aconductive brush, a conductive brush roller or a conductive plasticroller can be used. The discharging roller 37₅ is connected to an ACpower supply unit 38₅ which is an AC voltage supply means for supplyingAC voltage.

The AC power supply unit 38₅ is connected to the controller 39₅ which isa control means for controlling the AC power supply unit 38₅. Theconveyor belt 12₅ passes through this discharging roller 37₅ with therotation of the driving roller 16₅. The controller 39₅ controls the ACpower supply unit 38₅ to supply AC voltage to the discharging 37₅according to a preset program. As a result, the surface of the conveyorbelt 12₅ charged to plus and the back side charged to minus areneutralized. Thereafter, the conveyor belt 12₅ is moved to a beltcleaning device 22₅ in the neutralized state. Thus, when the conveyorbelt 12₅ is discharged and moved to the belt cleaning device 22₅, thebelt can be easily cleaned. Further, as a result of this discharging,the image transfer can be made under the same charged condition of theconveyor belt 12₅ and it is unnecessary to change transfer voltage in acontinuous image transfer.

As an example of application, it is possible to use the pinch roller 25₁described in the first embodiment as the discharging roller 37₅. In thiscase, as the characteristic of the pinch 25₁, a material having a highcoefficient of friction is needed and when a conductive rubber roller isused for the pinch roller 25₁, it becomes possible to construct a pinchroller which also serves as a discharging roller.

Further, in this case it is also necessary to make the pinch rollerbearing or the pinch roller holder using an electrically insulatedmaterial in order to prevent the discharging voltage from flowing to thedriving roller through the bearing.

As described in detail in the above, according to this fifth embodiment,it is possible to discharge the surface of the conveyor belt by a verysimple mechanism without generating ozone.

Next, a conveying means 200₆ in the sixth embodiment will be describedwith reference to FIGS. 12 to 16.

FIG. 12 shows the outline of the construction of a conveying means 200₆.Reference number 12₆ shows a conveyor belt, 16₆ shows a driving roller,17₆ shows a driven roller, 46₆ shows a regulation belt, 18₆ A and 18₆ Bshow a first compression spring and a second compression spring to givea tensile force to the conveyor belt 12₆, and 21₆ shows a driven rollerbearing. The regulation belt 46₆ is mounted or formed along an innerside at one end of the conveyor belt 12₆. The endless type conveyor belt12₆ is driven by the driving roller 16₆ and the driven roller 17₆. Thedriven roller 17₆ gives a tensile force to the conveyor belt 12₆ whenits bearing 21₆ is pressed by the first and the second compressionsprings 18₆ A and 18₆ B.

When a cause for generating a skid of the conveyor belt 12₆ wasinvestigated to reveal that it was largely affected by a difference inpressures generated by the first and the second compression springs 18₆A and 18₆ B. The results of this test are shown in FIGS. 13 and 14.

FIG. 13 shows the test result of amounts of skid per one turn of anendless type conveyor belt which was prepared by cutting a belt intoseveral pieces in trapezoidal shape intentionally giving differentperipheral lengths and connecting their ends to an endless conveyorbelt. The axis of abscissa shows differences in peripheral lengths atthe ends of a belt and the axis of ordinate shows amount of skid per oneturn of the belt.

In this test, for the purpose of making clear an effect of onlyperipheral length of the belt, a precisely prepared weight is used forgiving a tensile force to the belt. Further, the shorter peripherallength side was made as the plus side of skid direction of the belt. Asa result, it is seen that the larger a difference in peripheral lengthsbecomes, the larger the skid becomes. Furthermore, it is also seen thatthe skid progresses at the shorter peripheral length side of the belt.

On the other hand, shown in FIG. 14 is an amount of skid per one turn ofthe belt measured by changing a difference in loads applied at bothsides, and a difference in spring loads generating a tensile force isshown. The axis of abscissa shows differences in spring loads generatingtensile force and the axis of ordinate shows amount of skid per one turnof the belt on the axis of ordinates.

The graph in FIG. 14 shows "Difference in Spring Loads GeneratingTensile Force". In this test, for the purpose of conducting the test bymaking the load difference clear, a precisely prepared weight was used.

Further, for the purpose of investigating an effect of load differenceonly, a belt manufactured precisely in micron unit on an experimentalbasis was used. Further, the side of the belt having a larger tensileforce generating spring load applied was made as the plus side of skiddirection of the belt.

As a result, it is seen that the larger a load difference becomes, thelarger the degree of skid becomes correspondingly. Further, it is alsoseen that the skid of the belt progresses at the side with a larger belttensile force generating spring load.

Now, these two test results can be summarized as follows:

(1) The skid of the belt progresses at the short peripheral length side.

(2) The skid of the belt progresses at the large load side.

On the other hand, it is impossible to make the peripheral lengths ofthe conveyor belts 12₆ completely equal on all actual apparatus.Further, it is also impossible to completely eliminate fluctuations ofthe first and the second compression springs 18₆ A and 18₆ B.

It was decided to control the direction of skid of the conveyor belt 12₆based on the above results in this embodiment.

That is, as illustrated in FIG. 12, the endless type conveyor belt 12₆put ever the driving roller 16₆ and the driven roller 17₆ is made in theconstruction having a difference in its peripheral lengths at both sidesof L1>L2 when the peripheral lengths at both sides are L1 and L2.

As a means for giving a tensile force to the conveyor belt 12₆, atensioning mechanism 210₆ is composed of a first and a secondcompression springs 18₆ A and 18₆ B which are a first and a secondtensioning members. That is, the first compression spring 18₆ A having astrong pressure P1 is arranged at the shorter peripheral length L2 sideof the conveyor belt 12₆ and the second compression spring 18₆ B havinga weak pressure P2 (P1>P2) is arranged at the longer peripheral lengthL1 side.

As a result of this construction, the conveyor belt 12₆ skids always tothe first compression spring 18₆ A side having a strong pressure P1 atthe shorter peripheral length L2 side.

On the other hand, a regulation belt 46₆ is provided along theperipheral edge of the conveyor belt 12₆ with the second compressionspring 18₆ B having a weak pressure P2 arranged at the longer peripherallength L1 side. And, by bringing this regulation belt 46₆ in contactwith the end of the driven roller 17₆ (or the driving roller 16₆), theskid of the conveyor belt 12₆ is prevented.

The construction of this regulation belt 46₆ is as shown in FIGS. 15A to15C. That is, this regulation belt 46₆ is in the thick belt shape andprovided along the back side of the peripheral edge of the conveyor belt12₆ with the second compression spring 18₆ B arranged.

As the conveyor belt 12₆ always skids to the first compression spring18₆ A side having the strong pressure P1 at the shorter peripherallength L2 side, after a time "t" passed shown in FIG. 15B from theinitial state shown in FIG. 15A, the regulation belt 46₆ runs againstthe end of the driven roller 17₆ to prevent the further movement of theconveyor belt, which is then brought in the balanced state.

FIG. 16 shows the result of the skid of the conveyor belt when themeasures described above were not taken and FIG. 17 shows the result ofthe skid of the conveyor belt when the measures described above weretaken.

As the results of this test, running times of the belt shown in "TestTime (Second)" are plotted on the axis of abscissas and "RunningPosition (μm)" showing amounts of the skids of the belt are plotted onthe axis of ordinates.

As clear from these test results, the amount of the skid of the beltwhich was traveled without setting its mounting and pressure was large,the color shift of images on the image receiving medium 8 tends to occurin the direction perpendicular to the moving direction of the conveyorbelt 12₆. However, the skid of the conveyor belt is very small when thebelt was traveled with its mounting and pressure set, and it can be seenthat the conveyor belt 12₆ was in the stable running state scarcelycausing the color shift of images on the image receiving medium 8 in thedirection perpendicular to the moving direction of the conveyor belt12₆.

The test results shown in FIGS. 16 and 17 are one example. A furtherstatistic test revealed that the same effect is obtained up to adifference in peripheral lengths of 2 mm of both sides of a belt if adifference in pressures applied is suppressed to accuracy of 1 kgaccording to the construction in the sixth embodiment. Accuracy oflength ±0.01 mm and pressure ±50 g was demanded for a conventional beltand therefore, when a belt in this construction is used, it is possibleto effectively control and restrain the skid direction without demandinghigh accuracy.

As described above, the conveying means in the sixth embodiment iscapable of controlling the skid of the conveyor belt 12₆ in a verysimple construction.

Next, a conveying means 200₇ in the seventh embodiment will be describedwith reference to FIGS. 18 to 23.

As illustrated in FIGS. 18 and 19, a tapered roller 17₇ is used as adriven roller. This roller is tapered so that its diameter is increasedgradually to a large diameter from one end to another end. Theregulation belt 46₇ is positioned at the small diameter side of thetapered roller 17₇ and mounted along the back side of the peripheraledge of a conveyor belt 12₇ in the same manner as in FIGS. 15A to 15C.

When the conveyor belt 12₇ is put over driving roller 16₇ and thetapered roller 17₇ which is a driven roller, the conveyor belt 12₇ skidstoward the large diameter of the tapered roller 17₇.

In this case, on the conveyor belt 12₇ being pulled along the taperedroller 17₇, a tensile force F acting in the vertical direction is firstgenerated on its inclined portion, which is above the inclined portionof the tapered roller 17₇ as illustrated in FIG. 20. When the conveyorbelt 12₇ is moving, the tensile force F is divided into FH in the beltconveying direction and F_(V) in the vertical direction and thesedivided forces act on the conveyor belt. The direction F_(V) vertical tothe conveying direction of the belt is the direction toward the largediameter of the tapered roller 17₇ and the conveyor belt 12₇ is movedone-sidedly toward the direction of the large diameter of the taperedroller 17₇ by this force F_(V). That is, the direction of the skid ofthe conveyor belt 12₇ can be controlled using the tapered roller 17₇ asa driven roller.

If the direction of the skid can be controlled, a single piece of thebelt 46₇ is sufficient to restrain progress of the skid. That is, it canbe achieved by providing the regulation belt 46₇ only at the inside ofthe conveyor belt 12₇ at its small diameter side.

That is, the conveyor belt 12₇ skids toward the large diameter side butwhen the conveyor belt 12₇ moves one-sidedly for a certain amount, theskid regulation belt 46₇ is slid to the roller end surface of the smalldiameter side of the tapered roller 17₇, stopping the further skid at aposition where the skid force of the conveyor belt 12₇ is balanced withthe rubber repulsive force of the belt 46₇.

Once these forces are balanced each other, the conveyor belt 12₇ ismoved continuously in this balanced stated.

FIG. 21 shows a definite dimensional relation of the shape of thetapered roller 17₇ and the conveyor belt 12₇ which were used in theseventh embodiment. That is, the tapered roller 17₇ is 260 mm long andthe conveyor belt 12₇ put on this tapered roller 17₇ is 258 mm wide. Thediameter of the large diameter portion of this tapered roller 17₇ is22.3 mm and that of the small diameter portion is 21.9 mm. Therefore, asshown by the following expression, this tapered roller 17₇ has a taperof 0.001538.

    22.3-21.9/260=0.001538

FIG. 22 shows the test result of skid of the conveyor belt when nomeasures described above were taken and FIG. 23 shows the test result ofskid of the conveyor belt when the measures described above were taken.

As the result of this test, "Test Times (Sec.)" showing the runningtimes of the conveyor belt were plotted on the axis of abscissas and"Running Positions (μm)" showing amount of skid of the conveyor beltwere plotted on the axis of ordinates.

Therefore, the skid of the conveyor belt when it was moved withoutraking any measure is large while the color shift of images on the imagereceiving medium 8 tends to occur in the direction perpendicular to themoving direction of the conveyor belt 12₇. However, it is seen that theskid of the conveyor belt when it was moved with the tapered roller 17₇and the regulation belt 46₇ provided is very small and the belt ran inthe stable state scarcely causing the color shift of images on the imagereceiving medium 8 in the direction perpendicular to the movingdirection of the conveyor belt 12₇.

The tapered roller 17₇ shown in this seventh embodiment is not needed tobe applied as a driven roller, and when used as a third roller otherthan the driving roller 16₇ and the driven roller 17₇, its effect willnot be changed. Further, it is also not required to have the taperedroller 17₇ act from the inside of the conveyor belt 12₇ and its effectis not changed even when it was acted on the surface of the conveyorbelt 12₇.

Further, in this seventh embodiment the tapered roller 17₇ was describedas a driven roller and its small diameter side end surface was explainedas the surface contacting the regulation belt 46₇. However, not limitedto these usages, the end surface of the driving roller 16₇ may be usedas the skid prevention surface and even when a roller having an originalskid prevention surface is provided, its effect will not be changed.

As described above, the skid of the conveyor belt 12₇ can be controlledby a mechanism in very simple construction.

Next, a conveying means 200₈ in the eighth embodiment will be describedwith reference to FIGS. 24 to 28.

As illustrated in FIGS. 24 and 25, between the driving roller 16₈ andthe driven roller 17₈ arranged parallel to each other, there is adiagonal roller 50₈ arranged diagonally to these rollers 16₈ and 17₈.That is, it is arranged so that its one end 50₈ A is close to the drivenroller 17₈ and another end 50₈ B is close to the driving roller 16₈.

Further, this diagonal roller 50₈ is arranged slightly below the planesurface connecting a driving roller 16₈ and a driven roller 17₈ andfunctions as a skid moving direction control roller. A conveyor belt 12₈is put over these driving roller 16₈, the diagonal roller 50₈ and thedriven roller 17₈. On the other hand, a regulation belt 46₈ is providedalong the side edge of the conveyor belt 12₈ having a longer distancebetween the driving roller 16₈ and the diagonal roller 50₈. Theregulation belt 46₈ is in the construction as illustrated in FIGS. 15Ato 15C.

In the conveying means 200₈ in this construction, when moved, theconveyor belt 12₈ progressively skids toward the end having a shorterdistance between the diagonal roller 50₈ and the driving roller 16₈,that is, the conveyor belt 12₈ skids to the end 50₈ B of the diagonalroller 50₈.

As illustrated in FIG. 26, the conveyor belt 12₈ is first twisted by thediagonal roller 50₈ and a tensile force F is generated in the directionvertical to the central axis of rotation of the diagonal roller 50₈. Inactual operation, this force F is divided into two forces which act inthe belt conveying direction F_(H) and in the direction F_(V) verticalto the belt conveying direction. The direction F_(V) of the dividedforce is the direction for the shorter distance between the diagonalroller 50₈ and the driving roller 16₈ and by this force, the conveyorbelt 12₈ is given a force to move skiddingly in the direction of ashorter distance between the diagonal roller 50₈ and the driving roller16₈. That is, the conveyor belt 12₈ skids to the end 50₈ B side of thediagonal roller 50₈.

That is, it is possible to control the direction of skid of the conveyorbelt 12₈ by providing the diagonal roller 50₈ which is not parallel tothe driving roller 16₈.

If the direction of skid of the conveyor belt can be controlled, asingle piece of the regulation belt 46₈ which controls progress of theskid is able to create its effect. That is, this is achieved when thebelt 46₈ is provided only at the inside of the conveyor belt edge whichhas a long distance between the diagonal roller 50₈ and the drivingroller 16₈.

That is, the conveyor belt 12₈ skids to the side with a shorter distancebetween the diagonal roller 50₈ and the driving roller 16₈ according tothe diagonal roller 50₈. However, if the conveyor belt 12₈ movedskiddingly by a certain amount, the regulation belt 46₈ slides to theend surface of the driven roller 17₈ and the skid of the conveyor beltis stopped at a position where the skid moving force of the conveyorbelt 12₈ is balanced with the rubber repulsive force of the regulationbelt 46₈. Once both forces are balanced with each other, the conveyorbelt 12₈ continuously moves in this balanced state.

FIG. 27 shows the test result of the skid of the conveyor belt when nomeasures described above was taken and FIG. 28 shows the test resultwhen the measures described above were taken.

As the result of this test, "Test Times (Sec.)" showing the runningtimes of the conveyor belt were plotted on the axis of abscissas and"Running Positions (μm)" showing the amounts of the skids of theconveyor belt were plotted on the axis of ordinates.

Therefore, the skid of the conveyor belt without taking no measure islarge and the color shift of the images on the image receiving medium 8tends to occur in the direction perpendicular to the moving direction ofthe conveyor belt 12₈. However, the skid of the conveyor belt is verysmall when it was moved with the diagonal roller 50₈ and the regulationbelt 46₈ provided and it can be seen that the conveyor belt 12₈ wasrunning in the stable state scarcely causing the color shift on theimages on the image receiving medium 8 in the direction perpendicular tothe moving direction of the conveyor belt 8.

In this eighth embodiment, the diagonal roller 50₈ was arranged at theloose side of the conveyor belt 12₈. However, the effect of the diagonalroller 50₈ does not change even when the diagonal roller 50₈ is arrangedat the tension side of the conveyor belt if a space is available.

Further, it is not necessary to have the diagonal roller 50₈ act fromthe inside of the conveyor belt 12₈ and its effect does not change evenwhen the diagonal roller 50₈ is forced to act on the surface of theconveyor belt 12₈.

Further, the end surface of the driven roller 17₈ has been explained tobe the surface contacting the regulation belt 46₈ in this eighthembodiment. However, the end surface of the driving roller 16₈ may beused as the skid control surface or when a roller having an originalskid control surface is provided separately, its effect does not changeat all.

As described above, the skid of the conveyor belt 12₈ can be controlledby a system in very simple construction.

Next, a conveying means 200₉ in the ninth embodiment will be describedwith reference to FIGS. 29 to 34.

As illustrated in FIG. 29, the conveying means 200₉ is in theconstruction of L1>L2 when the peripheral lengths of both edges of anendless conveyor belt 12₉ put over the driving roller 16₉ and the drivenroller 17₉ are L1 and L2.

As a means to give a tension to the conveyor belt 12₉, a tensioningmechanism 210₉ is provided, which is composed of a first and a secondcompression springs 18₉ A and 18₉ B as a first and a second tensioningmembers, respectively. That is, the first compression spring 18₉ Ahaving a strong pressure P1 is arranged at the L2 side of a shortperipheral length of the conveyor belt 12₉ and the second compressionspring 18₉ B having a weak pressure P2 (P1>P2) is arranged at the L1side of the long peripheral length.

As described in the sixth embodiment, as a result of this construction,the conveyor belt 12₉ always skids toward the length L2 side where thecompression spring 18₉ A side having a strong pressure P1 is arranged.

On the other hand, a regulation plate 41₉ is provided along the edge ofthe conveyor belt 12₉ with the compression spring 18₉ A having a strongpressure P1 at the L2 side of a short peripheral length.

The regulation plate 41₉ kept in contact with the edge of the conveyorbelt 12₉ prevents the skid of the conveyor belt 12₉.

That is, as illustrated in FIGS. 30A to 30C, the regulation plate 41₉ isarranged to penetrate the rotary shaft of the driving roller 16₉. As theconveyor belt 12₉ always skids toward the first compression spring 18₉ Ahaving a strong pressure P1 at the L2 side of a short peripheral length,after elapsing "t" time shown in FIG. 30B, the edge of the conveyor belt12₉ runs against the surface of the regulation plate 41₉, preventing thefurther movement of the conveyor belt 12₉ and the conveyor belt 12₉ iskept in the balanced state.

FIG. 31 shows the state of skid of the conveyor belt when it was runwithout the belt mounting and pressure setting made as described aboveand FIG. 32 shows the same when the conveyor belt was run with the beltmounted and pressure setting made as described above. As the results ofthis test, "Test Times (Sec.)" showing the running time of the conveyorbelt is plotted on the axis of abscissas and "Running Positions (μm)"showing amount of skid of the belt is plotted on the axis of ordinates.

As clear from these test results, the amount of the skid of the conveyorbelt is large when it was run without belt mounting and pressure settingmade as described above and the color shift of the images on the imagereceiving medium 8 tends to occur in the direction perpendicular to themoving direction of the conveyor belt 12₉. However, it can be seen thatit is very small when the belt was run with the belt mounting andpressure setting made as described and the conveyor belt was in thestable running state with scarcely causing the color shift of the imageon the image receiving medium 8 in the direction perpendicular to themoving direction of the conveyor belt 12₉.

The test results shown in FIG. 31 and 32 are only one example. Furtherstatistical tests conducted revealed that the same results areobtainable according to the construction of the conveying means in thisninth embodiment if a difference in peripheral lengths of both sideedges of the belts is suppressed to 1.5 mm and a difference of pressuresapplied is suppressed to 0.8 kg. As for accuracy of the conveyor belt,±0.01 mm for length and ±50 g were so far demanded and therefore, whenthis construction is used, it is possible to effectively control andrestrain the direction of skid without demanding high accuracy for theconveyor belt.

FIG. 33 shows a conveying means 200₁₀ in the tenth embodiment. In orderto make the edges of a conveyor belt 12₁₀ and a regulation plate 41₁₀easy to slide, a surface 43₁₀ treated with a low frictional resistanceis provided in their contacting area. A test result of frictionalresistance of an unprocessed stainless steel plate with a PET film was0.665. On the other hand, the coefficient of friction of an ordinaryiron plate with a fluorine coating is 0.657 and therefore, it ispossible to obtain an equivalent coefficient of friction from a fluorinecoated iron plate even when an expensive stainless steel having a lowfrictional surface resistance is not used. Further, needless to say, amore low coefficient of frictional resistance can be obtained ifstainless steel is coated with fluorine.

FIG. 34 shows a conveying means 200₁₁ in the eleventh embodiment and asheet 44₁₁ of a low coefficient of friction is inserted between a skidcontrol plate 41₁₁ and the edge of a conveyor belt 12₁₁. The sheet 44₁₁of a low coefficient of friction is in somewhat large size and fixed tothe skid control plate 41₁₁ by fixing adhesive tape 45₁₁. Further, themethod for fixing the sheet 44₁₁ is not restricted and any other methodcan be used. In the embodiments 9 to 11, regulation plates. 41₉ to 41₁₁are provided to the driving rollers 16₉ to 16₁₁ but they may be providedto the driven rollers 17₉ to 17₁₁ or along the entire edge of theconveyor belts 12₉ to 12₁₁.

As described above, in the ninth to the eleventh embodiments, aneffective control of skid of the conveyor belt can be achieved when theconveyor belt 12₉ to 12₁₁ is so arranged that the conveyor belt isrunning while at least a part of it is kept in contact with theregulation plate 41₉ to 41₁₁.

Next, a conveying means 200₁₂ in the twelfth embodiment will bedescribed with reference to FIGS. 35 to 38.

As illustrated in FIGS. 35 and 36, a tapered roller 17₁₂ of whichdiameter becomes larger gradually from one end to another end is used asa driven roller. A regulation plate 41₁₂ is provided along one edge of adriving roller 16₁₂ at the same side as the large diameter side of thetapered roller 17₁₂.

When the conveyor belt 12₁₂ is put over the driving roller 16₁₂ and thetapered roller 17₁₂, which is a driven roller, the skid will progresstoward the larger diameter of the tapered roller 17₁₂ when the conveyorbelt is moved as described in the seventh embodiment.

That is, as illustrated in FIG. 36, a tensile force F vertical to theinclined portion that is the tapered portion of the tapered roller 17₁₂is first generated on the conveyor belt 12₁₂ being pulled along thetapered roller 17₁₂.

When the conveyor belt 12₁₂ is moving, this tensile force F is splitinto two: F_(H) acting in the belt conveying direction and F_(V) actingin the direction vertical to the belt conveying direction. The directionF_(V) of the split force vertical to the belt conveying direction is thedirection toward the larger diameter of the tapered roller 17₁₂ and bythis force F_(V), the conveyor belt 12₁₂ is moved one-sidedly in thedirection of the larger diameter of the tapered roller 17₁₂. That is,the direction of skid of the conveyor belt 12₁₂ is controlled using thetapered roller 17₁₂ as a driven roller and the movement is regulated bythe regulation plate 41₁₂ provided at the larger diameter side of thetapered roller 17₁₂.

When the skid of the conveyor belt 12₁₂ progressed to a certain amount,the regulation plate 41₁₂ and the outer edge or the conveyor belt slideand the skid is stopped at a position where the skid moving force of theconveyor belt 12₁₂ is balanced with a reactive force of the regulationplate 41₁₂. Once both forces are balanced, the conveyor belt 12₁₂ ismoved in this balanced state.

FIG. 37 shows the test result of the skid moving state when the conveyorbelt was run with no measure taken and FIG. 38 shows the test result ofthe skid moving state when the conveyor belt was run with the taperedroller 17₁₂ and the regulation plate 41₁₂ provided.

As the results of this test, "Test Times (Sec.)" showing running timesof the conveyor belt is plotted on the axis of abscissas and "RunningPosition (μm)" showing the amount of skid of the belt is plotted on theaxis of ordinates.

As can be seen from these test results, the amount of skid of theconveyor belt is large and the color shift of the images on the imagereceiving medium 8 tends to occur in the direction perpendicular to themoving direction of the conveyor belt when no measure was taken. But,the amount of skid is very small when the conveyor belt 12₁₂ was runwith the tapered roller 17₁₂ and the regulation plate 41₁₂ provided andthe conveyor belt is in the stable running state without scarcelycausing the color shift of the images on the image receiving medium 8 inthe direction perpendicular to the moving direction of the conveyorbelt.

The tapered roller 17₁₂ shown in the twelfth embodiment is notnecessarily to be used as a driver but can be used as a third rollerother than the driving roller 16₁₂ and the driven roller as its effectwill not be changed. Further, it is also not necessary to have thetapered roller 17₁₂ act from the inside of the conveyor belt and itseffect will not be changed even when it is acted on the surface side ofthe conveyor belt 12₁₂.

As described above, it is possible to efficiently suppress the skid ofthe conveyor belt by a system in very simple construction.

Next, a conveying means 200₁₃ in the thirteenth embodiment withreference to FIGS. 39 to 42.

As illustrated in FIGS. 39 and 40, there is a diagonal roller 50₁₃provided between a parallelly arranged driving roller 16₁₃ and a drivenroller 17₁₃ not parallelly but diagonally to these rollers 16₁₃ and17₁₃. That is, the diagonal roller is so arranged that one end 50₁₃ A ofthe diagonal roller 50₁₃ A is close to the driven roller 17₁₃ side andanother end 50₁₃ B is close to the driving roller 16₁₃. Furthermore,this diagonal roller 50₁₃ is arranged at a position somewhat below theplane surface connecting the driving roller 16₁₃ and the driven roller17₁₃ and functions as a skid control roller. The conveyor belt 12₁₃ isput over the driving roller 16₁₃, the diagonal roller 50₁₃ and thedriven roller 17₁₃. On the other hand, a regulation plate 41₁₃ isprovided along one side edge of the conveyor belt where a distancebetween the diagonal roller 50₁₃ and the driving roller 16₁₃ is short.The regulation plate 41₁₃ is in the construction as illustrated in FIGS.30A to 30C.

In the construction described above, the conveyor belt 12₁₃ movesone-sidedly toward the end of the diagonal roller 50₁₃ of which distanceto the driving roller 16₁₃ is short. That is, the conveyor belt 12₁₃moves one-sidedly toward the end 50₁₃ B of the diagonal roller 50₁₃.

In this case, as illustrated in FIG. 40, the conveyor belt 12₁₃ is firsttwisted by the diagonal roller 50₁₃ and a tensile force F is generatedin the direction perpendicular to the central axis of rotation of thediagonal roller 50₁₃. In actual operation, this force F is split andacts in the belt conveying direction FH and the direction F_(V) verticalto the belt conveying direction. The direction F_(V) of a force split inthe direction vertical to the belt conveying direction is a direction ofa short distance of the diagonal roller 50₁₃ to the driving roller 16₁₃and by this force the conveyor belt 12₁₃ is given a force to moveone-sidedly in the direction of a short distance of the diagonal roller50₁₃ to the driving roller 16₁₃. That is, the conveyor belt 12₁₃ movesskiddingly to the end 50₁₃ B side of the diagonal roller 50₁₃.

That is, it is possible to control the skid direction of the conveyorbelt 12₁₃ by providing the diagonal roller 50₁₃ which is not parallel tothe driving roller 16₁₃ and to control the further skid by theregulation plate 41₁₃.

In other words, the conveyor belt 12₁₃ moves skiddingly to the shortdistance side between the diagonal roller 50₁₃ and the driving roller16₁₃ following the diagonal roller 50₁₃ but when the conveyor belt 12₁₃moves skiddingly to a certain distance, the outer peripheral edge of theconveyor belt slides on the regulation plate 41₁₃ and the skid of thebelt is stopped at a position where the skidding force of the conveyorbelt 12₁₃ is balanced with the reaction of the regulation plate 41₁₃.Once both forces are balanced, the conveyor belt 12₁₃ moves continuouslywhile kept in this balanced state.

FIG. 41 shows the test result of the skid of the conveyor belt when themeasures described above were not taken and FIG. 42 shows the same withthe measures described above taken.

As the results of this test, "Test Time (Sec.)" showing the belt runningtimes is plotted on the axis of abscissas and "Running Positions (μm)"showing amount of skid of the belt is plotted on the axis of ordinates.

Therefore, skid of the conveyor belt arranged without taking any measureis large and the color shift of the images tends to occur on the imageson the image receiving medium 8 in the direction perpendicular to themoving direction of the conveyor belt 12₁₃. However, the skid of theconveyor belt 12₁₃ is very small when the diagonal roller 50₁₃ and theregulation plate 41₁₃ are arranged and it is seen that the conveyor belt12₁₃ is in the stable running state scarcely causing the color shift ofthe image on the image receiving medium 8 in the direction perpendicularto the moving direction of the conveyor belt.

In the thirteenth embodiment, the diagonal roller 50₁₃ was arranged atthe loose side of the conveyor belt 12₁₃. However, the effect of thediagonal roller 50₁₃ will not be changed even when it is arranged at thestretched side of the conveyor belt 12₁₃ if a space is available.

Further, it is not necessary to have the diagonal roller 50₁₃ act fromthe inside of the conveyor belt 12₁₃ and the effect of the diagonalroller 50₁₃ does not change when the diagonal roller 50₁₃ is forced toact on the surface side of the conveyor belt 12₁₃.

As described above, it is possible to suppress the skid of the conveyorbelt 12₁₃ by a system in very simple construction.

Next, a conveying means 200₁₄ in the fourteenth embodiment withreference to FIGS. 43 to 50.

Here, only those portions differing from the construction illustrated inFIG. 1 are referred to in the description of the first embodiment willbe described and the explanation of the same portions will be omitted.

FIGS. 43 and 44 show the state where a belt unit frame 58 is lifted by alifting lever in the image forming operation so that the photosensitivedrums 2Y, 2M, 2C and 2BK and the conveyor belt 12 are brought in contactwith each other in the prescribed state.

FIG. 45 shows the state where the lifting lever was lowered and theconveyor belt 12 was separated from the photosensitive drums 2Y, 2M, 2Cand 2BK. Under this state where the conveyor belt 12 is separated fromthe photosensitive drums 2Y, 2M, 2C and 2BK, the conveyor belt unitincluding the conveyor belt 12 can be pulled out of the body of theimage forming apparatus to the outside. If the image receiving medium 8is jammed in the apparatus, the belt unit including the conveyor belt 12is pulled out of the body of the apparatus to the outside when takingout this jammed image receiving medium 8.

The belt unit is supported by a first lifting lever 52 provided at thefront and rear sides of the paper supply side and a second lifting lever53 provided at the front and rear sides of the paper exit side, totalfour levers. The first lifting levers 52 provided at the front and therear sides illustrated in the figure are connected by a first rotatingshaft 54 and rotate at the same angle. Further, the second liftinglevers 53 at the front and the rear sides shown in the figure areconnected by the second rotating shaft 55 and rotate at the same angle.Further, the first lifting levers 52 and the second lifting levers 53are connected mutually at the front side and the rear side,respectively. The first rotating shaft 54 is provided with a handle 57at its end. The first rotating shaft 54 and second rotating shaft 55 aresupported in the rotatable state on the body of the apparatus. When thehandle 57 is rotated, the first rotating shaft 54 rotates and thus, thefirst lifting levers 52 at the front and the rear sides are rotated.When the first lifting lever 52 is rotated, the connecting link 56 ispulled in the rotating direction, and the second lifting lever 53 isrotated. The belt unit frame 58 is lifted to the photosensitive drums2Y, 2M, 2C and 2BK side when the first and the second lifting levers 52and 53 are rotated.

In the image forming, the image forming apparatus is kept in the statewhere the handle 57 is rotated, that is, the belt unit frame 58 islifted. The lifting levers have been designed to have lengths so thatthe conveyor belt 12 and the photosensitive drums 2Y, 2M, 2C and 2BK aremaintained in the prescribed state where they are kept in contact witheach other. In processing the jammed image receiving medium 8, when thehandle 57 is rotated in the reverse direction To make the lifting leverslevel, the belt unit frame 58 goes down and the photosensitive drums 2Y,2M, 2C and 2BK are separated from the conveyor belt 12 as illustrated inFIG. 45.

For a motor for driving the conveyor belt 12, an outer roller motor,which is in a construction that the motor body is contained in a rollerand its housing is rotated, was adopted. Hereinafter, this motor will bedescribed by referring it as a roller-in motor 61.

The conveyor belt 12 is put over a roller 61a, which is a rotatinghousing of the roller-in motor 61, and the driven roller 17, which isrotated with the movement of the conveyor belt.

First, the principle of the motor will be briefly described. FIG. 46 isa diagram showing Fleming's left hand rule and FIG. 47 is a diagramshowing the principle of a DC motor.

Motors called electric motors are all in a construction to run byconverting electric energy into mechanical energy and generating turningforce (torque) by electromagnetic force. The most basic electromagneticforce is according to Fleming's left hand rule illustrated in FIG. 46and when current I is flown through a conductor in length l placed inthe magnetic field B, a force F acting on the conductor is obtained.

A motor is manufactured on the basis of this principle and a DC motorillustrated in FIG. 47 rotates according to the principle describedbelow. When a current is applied to a coil in the magnetic field in thedirection shown in the figure, a downward force acts on a conductor xand an upward force acts on a conductor y and these conductors x, y arerotated clockwise. However, if this state is left as it is, thedirections of the downward and upward forces are reversed when theconductors x, y are rotated to the opposite side and they are notrotated. So, when the conductors x, y are moved from under the N pole tothe S pole and from under the S pole to the N pole, the currentdirection is reversed by a rectifier mechanism comprising commutatorsegments connected to the rotating conductors x, y and fixed brusheswhich are slide contacting the commutator segments, thus generatingturning forces in the same direction. Actual motors are in aconstruction that a number of conductors and commutator segments areprovided in order to increase the space utilization rate and to makegeneration of torque smooth and conductors are contained in the groovesof cores.

FIG. 48 shows a diagram of the principle of construction of a steppingmotor used in this fourteenth embodiment and FIG. 49 shows a diagram ofthe principle of operation of the stepping motor. The stepping motor isa motor that rotates one step at a time at a fixed angle to input pulseand is also called a pulse motor or a step motor. In FIG. 49, if thephase A only is excited, magnetic flux becomes maximum when the rotortooth comes under the tooth of the winding of phase A and the motorstops at the position (1). When the excitation is switched to the phaseB successively, a force acts in the arrow direction and the motor stopsat the position (2) and when snitched to the phase C, the motor proceedsto the position (3). Thus, the motor rotates a fixed step at a time (thebasic step) when the excitation of the phase A/B/C is repeated.

In this fourteenth embodiment, the roller-in motor which is composed ofthis stepping motor is used. To be concrete, this motor is in such aconstruction that the outer rotor is rotated with the motor shaft fixed.This motor is generally called as an outer rotor type motor. When thisouter rotor type motor is used, the outer rotor can be used as a roller.Further, the cross sectional area becomes small as the motor body ishoused in the roller but the depth of the motor can be extended to theroller length. Therefore, a more cross sectional area can be obtained byan area corresponding to the depth although magnetic flux of an innermagnet per unit becomes small. It is generally said that in order to getan increased torque that is obtained when the outer diameter of a motoris made double by extending the depth of the motor, three times of thedepth is needed. In the case of this embodiment, the outer rotor typemotor was in a shape of .o slashed.50×30 mm. As the driving roller is .oslashed.25×290 mm, the cross sectional area is 1/4 and the depth isabout 10 times. Now, to make it easy to think, when judging based on thesectional area of the driving roller, a length of 6×30 mm is requiredfor the depth from 2:3=4:X, X=6. That is, this means that a motor in .oslashed.50×30 mm and a motor in .o slashed.25×180 mm are able togenerate the same torque. In this embodiment, from a 290 mm long drivingroller, a motor in .o slashed.25×290 mm is able to have a torque of 1.6times of that of a motor in .o slashed.25×180 mm. Thus, by housing amotor in a roller, it is possible to increase a motor torque withouteffecting a size of an apparatus.

FIG. 50 shows a block diagram of the roller-in motor control. A systemcontroller 70 is for controlling the entire apparatus. A reference clockgenerator 71 generates a reference clock and a divider 72 divides thereference clock from the reference clock generator 71. A PLL circuit 73outputs driving pulses corresponding to a signal from the divider 72 andan encoder signal from the roller-in motor 61. A roller-in motorcontroller 74 controls the running of the roller-in motor by driving aroller-in motor driver 75 corresponding to the driving pulses from thePLL circuit 73. The divider 72 is used to generate clock widths that areeasily controllable by the roller-in motor 61. A rotary encoder 76 as arotary fluctuation detector is housed in the roller-in motor 61. The PLLcontrol is to control driving control waveforms and output waveformsfrom the encoder 76 so that they agree with each other.

As described above, when an outer rotor type motor housing the motorbody in the conveyor belt driving roller is used, it becomes possible toincrease the motor torque without affecting the image forming apparatus.Further, differing from conventional motors, there is no occupying areaat the outside of the conveyor belt and it becomes unnecessary to avoidthe motor cross sectional area when processing jammed papers and thereis a merit that image forming apparatus can be down sized.

According to this fourteenth embodiment, it is possible to eliminate anoccupying area for an independent motor and easily increase the motortorque when roller-in type conveyor belt driving motors are adopted.Furthermore, it is not necessary to evade the conveyor belt unit largelywhen processing jammed papers. Thus, an image forming apparatus whichdoes not become large in size.

Next, referring to FIGS. 51 through 60, a conveying means used in theimage forming means shown in FIG. 1 as the fifteenth embodiment will bedescribed.

First, the inventor conducted a test to control the one-sided movementof the conveyor belt being moved with a tapered roller. The outline ofthe test apparatus used in this test is shown in FIG. 51.

A conveying means 200₁₅ comprises a conveyor belt 12₁₅ for conveying animage receiving medium, a driving roller 16₁₅ for driving the conveyorbelt 12₁₅, a driven roller 17₁₅ having an inclined tapered surface, aregulation plate 41₁₅ arranged in the state movable in the directionparallel to the rotating center axis of the driving roller 16₁₅ and aone-sided moving force measuring sensor 19₁₅ for measuring one-sidedmoving force of the conveyor belt 12₁₅.

The endless type conveying belt 12₁₅ is put on the driving roller 16₁₅and the tapered driven roller 17₁₅, and turned around by the rotation ofthe driving roller 16₁₅. The tapered driven roller 17₁₅ generates atension on the conveying belt 12₁₅ as its bearing 21₁₅ is pushed outwardby a driven roller compression spring 18₁₅ which is a tension applyingmeans.

Now, if the driven roller 17₁₅ is a tapered roller, the conveyor belt12₁₅ gradually skids toward the small diameter side of the taperedroller or the large diameter side of the tapered roller. In this test,as the regulation plate 41₁₅ is arranged at the small diameter side ofthe driven roller 17₁₅, if the conveyor belt 12₁₅ gradually skids towardthe small diameter side of the driven roller 17₁₅, the one-sided movingforce obtained by the action of the conveyor belt 12₁₅ against theregulation plate 41₁₅ is measured by the one-sided moving forcemeasuring sensor 19₁₅. Further, the roller of the driven roller 17₁₅ hasbeen designed in the length longer than the width of the conveyor belt12₁₅ so that the taper effect will act on the overall width of theconveyor belt 12₁₅.

The slippage of the conveyor belt 12₁₅ is not necessarily taken placeregardless of the taper size of the tapered driven roller 17₁₅. Further,the slippage of the conveyor belt 12₁₅ is also affected by thecoefficient of friction of the tapered driven roller 17₁₅ with theconveyor belt 12₁₅. At the same time, it is also affected by the presscontacting state of the tapered driven roller 17₁₅ and the conveyor belt12₁₅, that is, a load applied on the conveyor belt.

So, in order to make these effects clear, the one-sided moving force wasmeasured based on three parameters shown below:

(1) Coefficient of static friction of the conveyor belt 12₁₅ with thedriven roller 17₁₅.

(2) Taper size of the driven roller 17₁₅.

(3) Load applied on the conveyor belt 12₁₅.

Now, definitions of the terms used will be clarified here.

The taper size is expressed in a value of a difference between thediameter D of the large diameter side of the driven roller 17₁₅ and thediameter d of the small diameter side divided by the length of theroller portion. That is, Taper T=(D-d)/L.

Further, change in coefficient of static friction was achieved bychanging the surface condition of the driven roller 17₁₅. The appliedload W of the conveyor belt 12₁₅ is a total value of sizes of the forcesacting from the driven roller compression springs 18₁₅ at both sides ofthe conveyor belt 12₁₅ arranged to apply the tensions to the conveyorbelt 12₁₅ as previously explained (the belt tension becomes W/2).

Further, the load applied on the conveyor belt was regulated byconversion of several kinds of the compression spring 18₁₅.

Now, sizes of respective parameters have been set as follows:

(1) Coefficient of friction:5 kinds of 0.24, 0.25, 0.26, 0.27 and 0.28.

(2) Taper size:5 kinds of 0.77×10⁻³, 1.54×10⁻³, 2.31×10⁻³, 3.08×10⁻³ and3.85×10⁻³

(3) Load applied to conveyor belt:5 kinds of 2.5 Kg, 2.75 Kg, 3.0 Kg,3.25 Kg and 3.5 Kg

The graphs showing these test results summarized are shown in FIGS. 52through 56.

The load applied to the conveyor belt is shown in respective graphs asthe load applied, and coefficient of static friction, taper size andsize of one-sided moving force of the conveyor belt are shown in the x,y and z axes, respectively.

What can be seen from these graphs are as follows:

(1) When a load applied to the conveyor belt is noted, the conveyor belt12₁₅ moves toward the small diameter side of the driven roller 17₁₅ at aload applied to the belt above 3 kg.

(2) When a coefficient of static friction is noted, the conveyor belt12₁₅ moves toward the small diameter side of the driven roller 17₁₅ at acoefficient of static friction below 0.26.

(3) When a taper size of the driven roller 17₁₅ is noted, the conveyorbelt moves toward the small diameter side of the tapered roller 16₁₅ ata taper size above 2.31×10⁻³.

(4) When a load applied to the conveyor belt is noted, if it is above 3kg, there is no change in the one-sided moving force pursuant to changein size of load applied to the belt and a nearly constant one-sidedmoving force is obtained.

(5) When a coefficient of static friction is noted, if it is below 0.26,there is no change in the one-sided moving force pursuant to change insize of coefficient of static friction and a nearly constant force isobtained.

(6) When a size of the driven roller 17₁₅ is noted, if it is above2.31×10⁻³, a change in the one-sided moving force corresponding to thechange in taper size is obtained.

Now, as to the phenomenon of (4), it can be explained as follows. Thatis, as the driving and driven rollers do not contact the conveyor belt12₁₅ closely if a load applied to the conveyor belt is less than 3 kgand the conveyor belt does not run stably, the one-sided movingdirection of the conveyor belt toward the driven roller 17₁₅ cannot becontrolled. On the other hand, if a load applied to the conveyor beltbecomes 3 kg, the rollers closely contact the conveyor belt 12₁₅ and theeffect of the driven roller 17₁₅ will depend on sizes of taper andcoefficient of static friction. If a load applied to the conveyor beltexceeds 3 kg, as a stabilized close contacting (slipping) state hasalready been produced between the driving and driven rollers and theconveyor belt 12₁₅, size of the one-sided moving force does not changein consonance with size of a load applied to the belt.

Next, as to the phenomenon of (5), it can be explained as follows. Thatis, if a coefficient of static friction is above 0.26, no stabilizedslipping state is produced between the conveyor belt 12₁₅ and the drivenroller 17₁₅. If a coefficient of static friction becomes 0.26, thestabilized slipping state is produced between the conveyor belt 12₁₅ andthe driven roller 17₁₅. This slip progresses toward the small diameterside of driven roller 17₁₅. If this coefficient of static friction isless than 0.26, as a stabilized slipping stage has already beenproduced, size of the one-sided moving force does not change inconsonance with size of coefficient of static friction.

Further, as to the phenomenon of (6), it can be explained as follows.That is, up to the taper size 2.31×10⁻³, a one-sided moving forceoriginal to the conveyor belt is larger than the taper size and is notcontrollable by the inclination of the taper. However, if the taper sizebecomes 2.31×10⁻³, a force of the conveyor belt to slip on the taperedportion becomes strong by its one-sided moving force and the one-sidedmoving force is governed by the taper direction not by the one-sidedmoving direction original to the conveyor belt. If the taper sizeexceeds 2.31×10⁻³, the slipping amount of the conveyor belt 12 becomesconspicuous in response to the taper size and a one-sided moving forcecorresponding to the taper size is obtained and the slip progressestoward the small diameter side of driven roller 17₁₅.

As described above in detail, when these results are summarized, if ataper size is made to above 2.31×10⁻³, the conveyor belt 12₁₅ and atapered roller which have a coefficient of static friction below 0.26are used and a load applied to the conveyor belt is regulated preferablyto above 3 kg, it becomes possible to control the one-sided movingdirection of the belt 12₁₅ toward the small diameter side of the drivenroller 17₁₅.

Next, to promote the stability to control the one-sided moving directionaccording to this system, a test was conducted using the TAGUCHI method.

This TAGUCHI Method is one test method of the quality controlengineering and it is a test method for selecting parameters comprisingan apparatus A for performing a motion B stably under a considerableoperating environment to the optimum condition when, for instance, theapparatus A performs the motion B.

That is, this method has a feature to economically create a functionthat is strong against noise by taking noise, which makes a functionworse, in positively when making an appraisal.

Taguchi Method makes use of a technique called "two-stage design byparameter." In the first-stage designing, a control factor and an errorfactor are extracted. These factors are assigned to an orthogonal array,according to which an experiment will be done to select an optimalcombination of parameters. The optimal parameters thus selected at thisstage mean their combination obtained from the viewpoint of at whichlevel should be selected the respective factors as obtained from theexperimental results at the first stage. That is, no experiment has beenreally performed by any actual combination of the parameters. Then adifference will be calculated out, from the experimental results at thefirst stage, between the optimal combination of the parameters and thegain given by a combination under actual conditions. The difference thuscalculated will be taken as a criterion. At the second stage both theexperiment by the combination of the parameters as actually chosen andthe experiment under the combination of current conditions will beperformed to calculate out the differential gain from these actualexperimental results. If the estimated difference in the first gain andthe differential gain coming out of the actual confirming experiment arealmost equivalent to each other, one can make sure that the experimenthad the reproducibility confirming that the parameters had beencorrectly chose. If, on the contrary, the difference is great betweenthe estimated differential gain in the first case and the gain resultingfrom the actual confirming experiment, one can evaluate that theexperiment has no reproducibility, that the combination has been made ofthe parameters susceptible to noise and finally that one could notobtain any optimal combination of parameters.

The outline of the test apparatus is shown in FIG. 57. If the conveyorbelt 12₁₅ moves toward the regulation plate 41₁₅ and pushes theregulation plate 41₁₅, this regulation plate pushes the fixed one-sidedmoving force measuring sensor 19₁₅ and thus, a force of the conveyorbelt 12₁₅ to push the regulation plate 41₁₅ can be measured. Theregulation plate 41₁₅ is in such a structure that it is possible to movein the direction perpendicular to the rotating shaft of the drivenroller 17₁₅.

Parameters used in the test are as follows. Control factors are fourkinds: (1) taper size, (2) load applied to the conveyor belt, (3)conveyor belt thickness and (4) applied load balance and values ofrespective factors are:

(1) Taper size=0×10⁻³, 2.31×10⁻³ and 3.85×10⁻³.

(2) Load applied to the conveyor belt=3.0, 3.5 and 4.0 kg.

(3) Conveyor belt thickness=75 and 100 μm.

(4) Applied load balance=10%, 20% and 30% increased at the largediameter side.

Further, error factors which cause noise were determined to be sixkinds: (1) temperature and humidity, (2) the surface conditions ofrollers, (3) variance in applied load, (4) parallelism of thephotosensitive drum shafts, (5) parallelism of the transfer rollershafts and (6) difference in peripheral lengths of the conveyor belt,and values of respective factors were determined as follows:

(1) Temperature and humidity=high temperature and high humidity (30°C.-85%), low temperature and low humidity (10° C.-20%).

(2) The surface condition of the rollers=no toner contamination, withtoner contamination.

(3) Dispersion of applied load=30% large at the small diameter side, 30%large at the large diameter side.

(4) Parallelism of the photosensitive drum shafts=0.2 mm upper stream atthe small diameter side, 0.2 mm upper stream at the large diameter side.

(5) Parallelism of the transfer roller shafts=0.2 mm upper stream at thesmall diameter side, 0.2 mm upper stream at the large diameter side.

(6) Difference in the peripheral lengths of the belt=long at the smalldiameter side, long at the large diameter side.

Further, the conveyor belt 12₁₅ in the different peripheral lengths ofboth edges was used in these tests. That is, when the peripheral lengthsof both edges are L1 and L2 as shown in FIG. 12, wherein the sixthembodiment is presented, the peripheral lengths were set at L1>L2 in thesixth embodiment. In this test, a case wherein L1 was set to be largerthan L2 (L1>L2) likewise the sixth embodiment and a case wherein L1 wasset at smaller than L2 (L1<L2) were adopted. Therefore, "Smallerdiameter side N short" described in the "f:Peripheral length differenceof both edges of the belt" column in Tables 2 and 3 shows that theperipheral length L1 corresponding to the small diameter side of thedriven roller 17₁₅ is shorter than the peripheral length L2corresponding to the large diameter side. "Small diameter side N Long"shows that the peripheral length L1 corresponding to the small diameterside of the driven roller 17₁₅ is longer than the peripheral length L2corresponding to the large diameter side.

Further, "Large diameter side upper stream" described in the Parallelismof the transfer roller shafts column shows the state that one end ofeach rotating shaft of the transfer rollers 5Y, 5M, 5C and 5BK (shown inFIG. 1) is one-sided to the direction of the large diameter side of thedriven roller 17₁₅. "Small diameter side upper stream" shows the statethat one end of each rotating shaft of the transfer rollers 5Y, 5M, 5Cand 5BK (shown in FIG. 1) is one-sided to the direction of the smalldiameter side of the driven roller 17₁₅.

Further, "Large diameter side upper stream" described in Parallelism ofthe photosensitive drum shafts column shows the state that one end ofeach rotating shaft of the photosensitive drums 2Y, 2M, 2C and 2BK(shown in FIG. 1) is one-sided toward the large diameter side of thedriven roller 17₁₅. "Small diameter side upper stream" shows the statethat one end of each rotating shaft of the photosensitive drums 2Y, 2M,2C and 2BK (shown in FIG. 1) is one-sided toward the small diameter sideof the driven roller 17₁₅.

Now, allocating these control factors at orthogonality L18 and the errorfactors at orthogonality LB, 144 tests were conducted by direct productaccording to the orthogonal array table.

Further, a force pushing the regulation plate 41₁₅ by the conveyor belt12₁₅ was used as the output values of the tests.

Now, the measured results are simplified and shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________    Error                                                                             f: Peripheral length                                                                     Small Small Small Small Small Small Small Small                factor                                                                            difference between                                                                       diameter                                                                            diameter                                                                            diameter                                                                            diameter                                                                            diameter                                                                            diameter                                                                            diameter                                                                            diameter                 both edges of belt                                                                       side/short                                                                          side/long                                                                           side/long                                                                           side/short                                                                          side/short                                                                          side/long                                                                           side/long                                                                           side/short               e: Parallelism of                                                                        Large Small Large Small Small Large Small Large                    roller shafts                                                                            diameter                                                                            diameter                                                                            diameter                                                                            diameter                                                                            diameter                                                                            diameter                                                                            diameter                                                                            diameter                            side upper                                                                          side upper                                                                          side upper                                                                          side upper                                                                          side upper                                                                          side upper                                                                          side                                                                                side upper                          stream                                                                              stream                                                                              stream                                                                              stream                                                                              stream                                                                              stream                                                                              stream                                                                              stream                   d: Parallelism of                                                                        Large Small Large Small Large Small Large Small                    photosensitive drum                                                                      diameter                                                                            diameter                                                                            diameter                                                                            diameter                                                                            diameter                                                                            diameter                                                                            diameter                                                                            diameter                 shafts     side upper                                                                          side upper                                                                          side upper                                                                          side upper                                                                          side upper                                                                          side upper                                                                          side                                                                                side upper                          stream                                                                              stream                                                                              stream                                                                              stream                                                                              stream                                                                              stream                                                                              stream                                                                              stream               c: Variance in Small diameter side                                                                       Large diamater side                                                                       Large diameter in                                                                         Small diameter side        applied load   large       large       lare        large                      b: Surface condition                                                                         With toner  No toner contamination                                                                    With toner  No toner                                                                      contamination              of roller      contamination           contamination                          a: Temperature &                                                                             High temperature/High humidity (30° C.--85%)                                                   Low termpature/Low humidity                                                   (10° C.-20%)                    humidity                                                                      __________________________________________________________________________    Control factor (L18)                                                             (1 Raw)  (2 Raw)                                                                              (3 Raw)     (4 Raw)                                        No.                                                                              C: Belt thickness                                                                      A: Taper size                                                                        B: Load applied to belt                                                                   D: Appoied load balance                                                                       N1                                                                              N2                                                                              N3                                                                              N4                                                                              N5                                                                              N6                                                                              N7                                                                              N8               __________________________________________________________________________     1  75 μm                                                                              0      3.0 kg      Large diameter side 10% increase                                                              ⊚                                                                X ⊚                                                                ⊚                                                                X X .circleincircle                                                               . .circleincirc                                                                 le.               2  75 μm                                                                              0      3.5 kg      Large diameter side 20% increase                                                              ⊚                                                                X ⊚                                                                ⊚                                                                X X .circleincircle                                                               . .circleincirc                                                                 le.               3  75 μm                                                                              0      4.0 kg      Large diameter side 30% increase                                                              ⊚                                                                X ⊚                                                                ⊚                                                                X X .circleincircle                                                               . .circleincirc                                                                 le.               4  75 μm                                                                              3.85 × 10.sup.-3                                                               3.0 kg      Large diameter side 10% increase                                                              ⊚                                                                X ⊚                                                                ⊚                                                                X X .circleincircle                                                               . .circleincirc                                                                 le.               5  75 μm                                                                              3.85 × 10.sup.-3                                                               3.5 kg      Large diameter side 20% increase                                                              ⊚                                                                X ⊚                                                                ⊚                                                                X X .circleincircle                                                               . .circleincirc                                                                 le.               6  75 μm                                                                              3.85 × 10.sup.-3                                                               4.0 kg      Large diameter side 30% increase                                                              ⊚                                                                X ⊚                                                                ⊚                                                                X X .circleincircle                                                               . .circleincirc                                                                 le.               7  75 μm                                                                              2.31 × 10.sup.-3                                                               3.0 kg      Large diameter side 20% increase                                                              ⊚                                                                X ⊚                                                                ⊚                                                                X X .circleincircle                                                               . .circleincirc                                                                 le.               8  75 μm                                                                              2.31 × 10.sup.-3                                                               3.5 kg      Large diameter side 30% increase                                                              ⊚                                                                X ⊚                                                                ⊚                                                                X X .circleincircle                                                               . .circleincirc                                                                 le.               9  75 μm                                                                              2.31 × 10.sup.-3                                                               4.0 kg      Large diameter side 10% increase                                                              ⊚                                                                X ⊚                                                                ⊚                                                                X X .circleincircle                                                               . .circleincirc                                                                 le.              10 100 μm                                                                              0      3.0 kg      Large diameter side 30% increase                                                              ⊚                                                                X ⊚                                                                ⊚                                                                ⊚                                                                X .circleincircle                                                               . .circleincirc                                                                 le.              11 100 μm                                                                              0      3.5 kg      Large diameter side 10% increase                                                              ⊚                                                                X ⊚                                                                ⊚                                                                ⊚                                                                X .circleincircle                                                               . .circleincirc                                                                 le.              12 100 μm                                                                              0      4.0 kg      Large diameter side 20% increase                                                              ⊚                                                                X ⊚                                                                ⊚                                                                ⊚                                                                X .circleincircle                                                               . .circleincirc                                                                 le.              13 100 μm                                                                              3.85 × 10.sup.-3                                                               3.0 kg      Large diameter side 20% increase                                                              ⊚                                                                X ⊚                                                                ⊚                                                                ⊚                                                                X .circleincircle                                                               . .circleincirc                                                                 le.              14 100 μm                                                                              3.85 × 10.sup.-3                                                               3.5 kg      Large diameter side 30% increase                                                              ⊚                                                                X ⊚                                                                ⊚                                                                ⊚                                                                X .circleincircle                                                               . .circleincirc                                                                 le.              15 100 μm                                                                              3.85 × 10.sup.-3                                                               4.0 kg      Large diameter side 10% increase                                                              ⊚                                                                X ⊚                                                                ⊚                                                                ⊚                                                                X .circleincircle                                                               . .circleincirc                                                                 le.              16 100 μm                                                                              2.31 × 10.sup.-3                                                               3.0 kg      Large diameter side 30% increase                                                              ⊚                                                                ⊚                                                                ⊚                                                                ⊚                                                                ⊚                                                                X .circleincircle                                                               . .circleincirc                                                                 le.              17 100 μm                                                                              2.31 × 10.sup.-3                                                               3.5 kg      Large diameter side 10% increase                                                              ⊚                                                                ⊚                                                                ⊚                                                                ⊚                                                                ⊚                                                                X .circleincircle                                                               . .circleincirc                                                                 le.              18 100 μm                                                                              2.31 × 10.sup.-3                                                               4.0 kg      Large diameter side 20% increase                                                              ⊚                                                                ⊚                                                                ⊚                                                                ⊚                                                                ⊚                                                                X .circleincircle                                                               . .circleincirc                                                                 le.              __________________________________________________________________________

As explained above, a one-sided moving force (unit:g) was used to showthe output values in the actual tests. However, as the explanation willbe specialized even when numerical values are presented, the results arenot shown in numerical values of the measured one-sided moving force butare shown by whether the one-sided moving direction could be controlled.That is, if the one-sided moving direction occurred by the skid of theconveyor belt 12₁₅ toward the small diameter of the driven roller 17₁₅can be controlled when the conveyor belt was conveyed under theparameter conditions shown in the orthogonal array table, the one-sidedmoving force is measured as a result. In this case, the results areshown by ⊚ (a double circle) mark in Table 2.

On the other hand, if the conveyor belt 12₁₅ does not move toward thesmall diameter side of the driven roller 17₁₅ when the conveyor belt isconveyed under the parameter conditions shown in the orthogonal arraytable, the one-sided moving force is not measurable as a result. In thiscase, the results are shown with an X mark in the table 1.

Next, a dispersion analysis Table of applied load balance that wascalculated base on the one-sided moving force measured values obtainedin this test is shown as Table 2.

                                      TABLE 2                                     __________________________________________________________________________    Control factor                                                                           f: Degree of freedom                                                                     S: Square total                                                                       V: Variance                                                                          ρ %: Rate of contribution            __________________________________________________________________________    Applied load balance                                                                     2          37.05   18.53  17.98                                    __________________________________________________________________________

In this Table 2, the contribution rate is 17.98% and it can be seen thatthe influence rate is high.

Next, the effects of factors of the applied load balance calculatedbased on the one-sided moving force measured by this test are shown inFIG. 58. In this graph, the x-axis shows sizes of parameters of theapplied load balance and the y-axis shows the calculated results of S/Nradio. That is, this graph shows that the more S/N ratio is high, themore stability is high.

S/N ratio or Signal-to-noise ratio involves the quantification of thestability of respective functions. It is defined by the formula belowthat represents the ratio of function (request output signal) to noise.A large SN ratio implies a great function (request output signal) or alittle noise, or both, which ensures a stable state. Conversely, a smallSN ratio means a small function (request output signal) or a largenoise, or both, which signifies an unstable status.

    S/N ratio=Function (request output signal)/noise

Then, gains obtainable under the current condition and the optimumcondition were calculated. Further, the applied load balance wascalculated by selecting a case wherein the applied load balance wasincreased by 10% at the large diameter side. As seen in FIG. 58, this isthe lowest value in the test conducted this time and it has been knownthat better conditions are obtainable if the balance is increased by 20%and 30%.

Estimated gain under the optimum condition:11.371 db

Estimated gain under the current condition:6.192 db

From the above figures, a difference between the gains is: A differencein gains under the current and the

    ______________________________________                                        optimum conditions = 11.371 - 6.192 = 5.179 db                                10logX = 5.179                                                                where,                                                                        X = 10.sup.0.5179 = 3.30                                                      ______________________________________                                    

That is, it can be seen that the reliability can be improved to 3.3times of that under the current condition if the optimum condition (thestate with the applied load balance increased 10% at the large diameterside) is adopted.

Next, a checking tests were conducted under both the optimum conditionand the current condition. This test is to check if the estimatedreliability improvement can be really achieved.

The measured results are simplified likewise Table 1 shown above andpresented as Table 3.

                                      TABLE 3                                     __________________________________________________________________________    Error                                                                             f: Peripheral length                                                                     Small Small Small Small Small Small Small Small                factor                                                                            difference between                                                                       diameter                                                                            diameter                                                                            diameter                                                                            diameter                                                                            diameter                                                                            diameter                                                                            diameter                                                                            diameter                 both edges of belt                                                                       side/short                                                                          side/long                                                                           side/long                                                                           side/short                                                                          side/short                                                                          side/long                                                                           side/long                                                                           side/short               e: Parallelism of                                                                        Large Small Large Small Small Large Small Large                    transfer roller shafts                                                                   diameter                                                                            diameter                                                                            diameter                                                                            diameter                                                                            diameter                                                                            diameter                                                                            diameter                                                                            diameter                            side upper                                                                          side upper                                                                          side upper                                                                          side upper                                                                          side upper                                                                          side upper                                                                          side                                                                                side upper                          stream                                                                              stream                                                                              stream                                                                              stream                                                                              stream                                                                              stream                                                                              stream                                                                              stream                   d: Paralellism of                                                                        Large Small Large Small Large Small Large Small                    photosenstive drum                                                                       diameter                                                                            diameter                                                                            diameter                                                                            diameter                                                                            diameter                                                                            diameter                                                                            diameter                                                                            diameter                 shafts     side upper                                                                          side upper                                                                          side upper                                                                          side upper                                                                          side upper                                                                          side upper                                                                          side                                                                                side upper                          stream                                                                              stream                                                                              stream                                                                              stream                                                                              stream                                                                              stream                                                                              stream                                                                              stream               c: Variance in Small diameter side                                                                       Large diamater side                                                                       Large diameter side                                                                       Small diameter side        applied load   large       large       large       large                      b: Surface condition                                                                         With toner  No toner contamination                                                                    With toner  No toner                                                                      contamination              of roller      contamination           contamination                          a: Temperature &                                                                             High temperature/High humidity (30° C. -                                                       Low termpature/Low humidity                                                   (10° C. - 20%)                  humidity                                                                      __________________________________________________________________________    Control factor (L18)                                                               (1 Row)  (2 Row)                                                                              (3 Row)     (4 Row)                                      No.  C: Belt thickness                                                                      A: Taper size                                                                        B: Load applied to belt                                                                   D: Applied load balance                                                                   N1                                                                              N2                                                                              N3                                                                              N4                                                                              N5                                                                              N6 N7                                                                              N8                __________________________________________________________________________    Optimum                                                                            100 μm                                                                              2.13 × 10.sup.-3                                                               3.5 kg      Rear 10% increase                                                                         ⊚                                                                ⊚                                                                ⊚                                                                ⊚                                                                ⊚                                                                ⊚                                                                 ⊚                                                                .circleincircl                                                                e.                Current                                                                            100 μm                                                                              0      3.0 kg      0           X X ⊚                                                                ⊚                                                                ⊚                                                                X  ⊚                                                                X                 __________________________________________________________________________

As explained above, the one-sided moving force (unit:g) was used forindicating output values in the actual tests. However, as theexplanation will become the specialized one even when numerical valuesare presented, it is shown whether the one-sided moving direction couldbe controlled instead of results of obtained one-sided moving forceexpressed in numerical values. That is, when the conveyor belt 12₁₅ wasmoved under the parameter conditions shown in the orthogonal arraytable, the conveyor belt 12₁₅ is moved toward the small diameter side ofthe driven roller 17₁₅, and the one-sided moving force is measured asthe result. In this case, the results are shown by ⊚ (a double circle)mark in Table 3.

Next, the gains obtained under the current condition and the optimumcondition in this checking tests were calculated. Further, thecalculation was made by selecting the applied load balance increased by10% at the large diameter side. This is the lowest value in the test ofthis time as seen in FIG. 58 and it has been known that betterconditions can be obtained if the applied load balance is increased by20% and 30%.

Gain under the optimum condition:18.93 db

Gain under the current condition:12.04 db

From the above figures, a difference between them is:

A difference between gains under the current condition

    ______________________________________                                        and the optimum condition = 18.93 db - 12.04 db = 6.89 db                     10logX = 6.89                                                                 Therefore,                                                                    X = 10.sup.0.5179 = 4.9                                                       ______________________________________                                    

That is, it was confirmed that the high reliability of 4.9 times of thatunder the current condition (without applied load balance), which islarger than the estimated reliability improving rate 3.3 time, can beobtained.

As described above in detail, when the results are summarized, itbecomes possible to control the one-sided moving direction of theconveyor belt 12₁₅ so that the conveyor belt 12₁₅ is one-sided stablytoward the small diameter side of the driven roller 17₁₅ if the tapersize is made more than 2.31×10⁻³, the conveyor belt 12₁₅ and the drivenroller 17₁₅ of coefficient of static friction 0.26 or less are used, theapplied load at the large diameter side is increased by more than 10% ofthe applied load at the small diameter side and preferably, a loadapplied to the conveyor belt is set at more than 3 kg.

Further, it is preferable to apply load to the conveyor belt 12₁₅ atless than 6 kg. If more than 6 kg load is applied to the conveyor belt12₁₅, a coefficient of friction between the conveyor belt 12₁₅ andtapered driven roller 17₁₅ increases so that the conveyor belt 12₁₅tends to skid toward the large diameter side of the tapered drivenroller 17₁₅. Further, if more than 6 kg load is applied to the conveyorbelt 12₁₅, the conveyor belt 12₁₅ will be broken since the applied loadis too large for the conveyor belt 12₁₅. Therefore, it is preferable toapply a load to the conveyor belt 12₁₅ at 3 to 6 kg, and to control theone-sided moving of the conveyor belt 12₁₅ so that the conveyor belt12₁₅ is moved toward the small diameter side of the tapered drivenroller 17₁₅.

Now, the control of a zigzag running and one-sided moving direction andthe zigzag running control method using a zigzag running regulationplate involved in the fifteenth embodiment will be explained.

As explained above, it is possible to stably control the one-sidedmoving direction of the conveyor belt 12₁₅ using the driven roller 17₁₅comprising a tapered roller satisfying the above conditions and theapplied load balance. According to this tapered roller system, theone-sided moving direction of the conveyor belt 12₁₅ will become at thesmall diameter side of the driven roller 17₁₅. As a method to controlthe zigzag movement using this nature, there is a system using theregulation plate 41₁₅ as shown in FIG. 59. The conveying means 200₁₅shown in FIG. 59 comprises the conveyor belt 12₁₅ for conveying an imagereceiving medium, the driving roller 16₁₅ for driving the conveyor belt12₁₅, the tapered driven roller 17₁₅ both ends of which diametersdiffers and the regulation plate 41₁₅ which is a zigzag movingregulation plate. The endless shape conveyor belt 12₁₅ is put on thedriving roller 16₁₅ and the tapered driven roller 17₁₅ to be pulledaround by the rotation of the tapered driven roller 17₁₅ driven inaccordance with the rotation of the driving roller 16₁₅. As shown inFIG. 57, driven roller holders 21_(15A) and 21_(15B) of the tapereddriven roller 17₁₅ are pressed outward. This gives a tensile force tothe conveyor belt 12₁₅. As explained above, a compression spring18_(15A) pressing the small diameter side driven roller holder 21_(15A)and a compression spring 18_(15B) pressing the large diameter sidedriven roller holder 21_(15B) of the tapered driven roller 17₁₅ havebeen given with a difference of the belt compression force more than10%. In the case of this embodiment, as the large diameter side of thetapered driven roller 17₁₅ is arranged at the inner part in FIG. 59 andthe small diameter side is arranged at this side, the compression spring18_(15B) pressing the driven roller holder 21_(15B) at the largediameter side of the tapered driven roller 17₁₅ is given with acompression force 10% higher than the compression spring 18_(15A)pressing the driven roller holder 21_(15A) at the small diameter side ofthe tapered driven roller 17₁₅. Further, this tapered driven roller 17₁₅has a taper size more than 2.31×10⁻³ and as described above, its smalldiameter side of the tapered roller is at this side in FIG. 59 and thelarge diameter side is at the inner part. Further, the roller surface ofthis tapered driven roller 17₁₅ has been machined so that a coefficientof static friction between the tapered driven roller 17₁₅ and theconveyor belt 12₁₅ will become less than 0.26. Further, the compressionsprings 18_(15A) and 18_(15B) have been adjusted so that a total appliedload at this side and the inner side in FIG. 59 will become more than 3kg. On the other hand, the regulation plate 41₁₅ has been arranged inthe fixed state at this side of the driving roller 16₁₅ (at the smalldiameter side of the tapered driven roller 17₁₅ and the less appliedload side of the conveyor belt) in FIG. 59.

The state of the conveyor belt 12₁₅ in the construction described abovewhen operated is as follows. When the conveyor belt 12₁₅ is conveyed bythe rotation of the driving roller 16₁₅, the conveyor belt 12₁₅ isgradually one-sided to the small diameter side of the tapered drivenroller 17₁₅, that is, to this side in FIG. 59. When the one-sidedmovement of the conveyor belt 12₁₅ progresses, it contacts theregulation plate 41₁₅ which is arranged in the fixed state at this sideof the driving roller 16₁₅ in FIG. 59 and is conveyed while constantlysliding. As the regulation plate 41₁₅ is fixed in the stationary state,when the conveyor belt 12₁₅ has one-sided for a certain amount, a forceto press the regulation plate 41₁₅ and a reaction generated therefromare balanced against each other and the one-sided movement is stopped.On the other hand, as the zigzag running force of the conveyor belt 12₁₅is generally less than its one-sided moving force, the zigzag runningforce is included in the one-sided moving force and the reaction forcewhen these forces are balanced and the zigzag running of the conveyorbelt is not taken place. The test was conducted to measure the zigzagand one-sided movements of the conveyor belt 12₁₅ in the constructiondescribed above and the result is shown in FIG. 60.

That is, the one-sided moving direction of the conveyor belt 12₁₅ can becontrolled by the regulation plate 41₁₅ arranged at the small diameterside of the tapered driven roller 17₁₅. By this means, it becomespossible to suppress the progress of the one-sided movement and zigzagrunning of the conveyor belt.

As described above, when the taper size is set at more than 2.31×10⁻³,the conveyor belt 12₁₅ and the tapered driven roller 17₁₅ having acoefficient of static friction 0.26 or less are used, preferably appliedload at the large diameter side is increased by 10% more than that ofthe small diameter side and further, preferably applied load to theconveyor belt is increased to above 3 kg, it becomes possible to controlthe one-sided moving direction of the conveyor belt 12₁₅ so that itmoves stably toward the small diameter side of the tapered driven roller17₁₅. Further, when the regulation plate 41₁₅ is provided at the smalldiameter side of the tapered driven roller 17₁₅ at the same time, itbecomes possible to suppress the one-sided movement and the zigzagrunning of the conveyor belt with the high reliability.

The conveying means 200₁₅ concerning the fifteenth embodiment will befurther described.

Now, the rotating shafts of plural photosensitive drums 2Y, 2M, 2C and2BK shown in FIG. 1 have been constructed parallel with each other.Further, the rotating shaft of the driving roller 16₁₅ has been arrangedparallel to the rotating shafts of plural photosensitive drums 2Y, 2M,2C and 2BK.

On the other hand, the rotating shaft of the tapered shape driven roller17₁₅ has not been constructed parallel to the rotating shafts of thephotosensitive drums 2Y, 2M, 2C and 2BK and the driving roller 16₁₅. Ifthe rotating shaft of the driven roller 17₁₅ is parallel to the rotatingshaft of the driving roller 16₁₅ which is kept parallel to the rotatingshafts of the photosensitive drums, as the driven roller 17₁₅ is in thetapered shape, the ridge line of the large diameter side of the drivenroller 17₁₅ does not become parallel to the ridge line of its smalldiameter side and therefore, a difference is produced in the distancesthat are formed by both ridge lines with the photosensitive drums.Concretely, if the ridge line formed by the large diameter side of thedriven roller 17₁₅ with the driving roller 16₁₅ is so constructed thatit is kept contacted with the photosensitive drums, when the rotatingshaft of the driving roller 16₁₅ is positioned parallel to the rotatingshaft of the driven roller 17₁₅, the ridge line formed by the smalldiameter side of the driven roller 17₁₅ and the driving roller 16₁₅ doesnot contact the photosensitive drums. This is because the driven roller17₁₅ is in the tapered shape having a difference at both ends of theroller to its diameter. As the conveyor belt 12₁₅ is put over thedriving and driven rollers along this ridge line, an image receivingmedium conveyed by the conveyor belt 12₁₅ while being adsorbed does notcontact the photosensitive drums at its part (the small diameter side)and as a result, is not able to transfer a toner image formed on thephotosensitive drums even when transfer bias is applied.

So, the driven roller 17₁₅ has been so constructed that it does not havethe rotating shaft parallel to the driving roller 16₁₅. When assumingthat the large diameter of the driven roller 17₁₅ is D, the smalldiameter is d and the roller length is L, this driven roller 17₁₅ iskept in the state wherein the large diameter side is inclined to thelower side by an angle θ which is obtained from the followingexpression:

    tan θ={(D-d)/2}/L

When the rotating shaft of the driven roller 17₁₅ is positioned parallelto the rotating shaft of the driving roller 16₁₅, the inclination θ ofthe upper roller ridge at the photosensitive drum side of the drivenroller 17₁₅ is obtained as follows. First, a difference (D-d) betweenthe roller diameter D at the large diameter side and the roller diameterd at the small diameter side becomes a difference in the directionperpendicular to the driven roller 17₁₅. Then, when the roller length ofthe driven roller 17₁₅ is assumed to be L, tan θ={(D-d)/2}/L is obtainedas an upper inclination of the driven roller 17₁₅. Now, when therotating shaft of the driven roller 17₁₅ and the rotating shaft of thedriving roller 16₁₅ are arranged parallel to each other, the largediameter side of the driven roller 17₁₅ is inclined toward the upperside by an angle θ that is obtained above. So, if the large diameterside of the driven roller 17₁₅ is arranged by inclining to the lowerside, the upper surface of the driving roller 16₁₅ and the upper surfaceof the driving roller 16₁₅ become parallel to the plane surface formedat the transfer position of the photosensitive drum (parallel with theplane surface formed by the rotating shaft of the photosensitive drum)and an image receiving medium conveyed by the conveyor belt 12₁₅proportional to this plane surface contacts each of the photosensitivedrums at respective transfer positions and a good toner picture withoutimproper transfer is obtained.

Next, a test was conducted for the difference in the effect by Young'smodulus in the conveying direction of the conveyor belt 12₁₅ (Young'smodulus in the direction to be pressed by the regulation plate) based onthe test result described above. This test was conducted according tothe test method shown in FIG. 59 using the conveyor belts 12₁₅ withYoung's modulus changed and the state of the sliding edges of theconveyor belts 12₁₅ when the belts were run 300,000 times while keptcontacting the regulation plate 41₁₅ were compared. The results of thistest are shown in Table 4. Further, ◯ (circle) mark in the table showsthe belt 12₁₅ caused no problem and X mark shows the belt 12₁₅ causedsuch problems as crack, deformation, etc. on the sliding edge.

                  TABLE 4                                                         ______________________________________                                        Young's                                                                       modulus  100    150    200  250  300  350  400  450                           ______________________________________                                        Result   X      X      ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯                 ______________________________________                                    

When Young's modulus was 100 kg/mm², a phenomenon wherein the slidingedge of the belt 12₁₅ was turned up and elongated was caused as a resultof sliding with the regulation plate 41₁₅. As a result of thisphenomenon, the conveyor belt 12₁₅ ran in a zigzag direction because ofthe turned up edge although it was checked by the regulation plate 41₁₅and in an extreme example, the belt 12₁₅ was broken. Further, whenYoung's modulus was 150 kg/mm², a phenomenon was also caused, whereinthe sliding edge of the belt 12₁₅ was turned up and elongated as aresult of sliding with the regulation plate 41₁₅.

On the other hand, in the case of Young's modulus 200 kg/mm², burr,chip, etc. were not produced on the edge sliding with the regulationplate 41₁₅ and a good running was obtained. From this test result, itmay be said that the proper Young's modulus in the directionperpendicular to the conveying direction of the belt 12₁₅ is above 200kg/mm².

Further, Young's modulus of this conveyor belt 12₁₅ is that of materialcomprising single layer belts, coated multi-layer shaped belts,multi-layer structures including adhesive layers and is not anindividual Young's modulus of materials comprising the belt 12₁₅.

Next, a test for difference in the effect depending on difference inwidth of the belt 12₁₅ was conducted based on the test results describedabove. The width of the belt 12₁₅ is a length of the belt 12₁₅ in thedirection perpendicular to the conveying direction of the belt 12₁₅.

This test was conducted according to the test method shown in FIG. 59using the belts 12₁₅ in different widths for checking whether theone-sided movement of the belt 12₁₅ is effectively controlled to thedirection of the regulation plate 41₁₅ shown at this side in FIG. 59.

The results of this test are shown in Table 5. Further, ◯ (circle) markin the table shows no problem and X mark shows the one-sided movementdirection of the conveyor belt 12₁₅ being couldn't effectively.

                  TABLE 5                                                         ______________________________________                                        Width of the                                                                  conveyor belt                                                                 (mm)      10    20    30  40  50  60  70  200  300  500                       ______________________________________                                        Result    X     X     X   X   ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                      ◯                                                                      ◯             ______________________________________                                    

When the belt width was less than 40 mm, the one-sided moving directionof the belt 12₁₅ couldn't be controlled effectively because of thenarrow area of the driven roller 17₁₅ acting on the belt 12₁₅. On theother hand, in the case of the belt of which width is more than 50 mm,the test was conducted for the belt width of every 10 mm above 50 mm upto 500 mm and as a result, the one-sided moving direction could becontrolled effectively. This result indicates that the one-sided movingdirection of the belt is controllable when it is running under theconditions described above regardless of the belt width if the area ofthe driven roller 17₁₅ acts on the belt 12₁₅.

According to this test results, it may be said that the proper length ofthe belt 12₁₅ in the direction perpendicular to its running direction(the belt width) is more than 50 mm.

Next, referring to FIGS. 61 through 63B, the control of the one-sidedmoving direction in the sixteenth embodiment and a conveying means 200₁₆using a regulation belt, which is a zigzag running regulation memberprovided to the conveyor belt, will be described. As described above indetail, it is possible to control the one-sided moving direction of theconveyor belt using the tapered driven roller which has the samecondition as the tapered driven roller 17₁₅ in the fifteenth embodimentand the conveyor belt applied load balance. According to this systemusing the tapered driven roller and the conveyor belt applied loadbalance, the conveyor belt is one-sided toward the small diameter sideof the tapered driven roller. As a method to suppress the zigzagrunning, there is a system to use a regulation belt as shown in FIG. 61.The conveying means 200₁₆ comprises a conveyor belt 12₁₆ for conveyingan image receiving medium, a driving roller 16₁₆ for driving theconveyor belt 12₁₆, a driven roller 17₁₆ having an inclined taperedsurface and a regulation belt 46₁₆ provided at the large diameter sideof the tapered driven roller 17₁₆ in one united body with the conveyorbelt 12₁₆. The regulation belt 46₁₆ is in the same construction as thatin the sixth, seventh and eighth embodiments described above.

The endless type conveying belt 12₁₆ is put on the driving roller 16₁₆and the tapered driven roller 17₁₆, and turned around by the rotation ofthe driving roller 16₁₆. Tapered roller holders 21_(16A) and 21_(16B) ofthe tapered driven roller 17₁₆ are pressed outward by compressionsprings 18_(16A) and 18_(16B). This gives a tensile force to theconveyor belt 12₁₆. The compression spring pressing the driven rollerholder 21_(16A) at the small diameter side of the tapered driven roller17₁₆ and the compression spring 18_(16B) pressing the driven rollerholder 21_(16B) at the large diameter side of the tapered driven roller17₁₆ are given with a more than 10% difference of belt compressionforce. In the case of this sixteenth embodiment, as the large diameterside of the tapered driven roller 17₁₆ is arranged at the inner part inFIG. 61 and the small diameter side is arranged at this side in FIG. 61,the compression spring 18₁₆ pressing the driven roller holder 21_(16B)at the large diameter side of the tapered driven roller 17₁₆ has acompression force 10% higher than the compression spring 18_(16A)pressing the driven roller holder 21_(16A) at the small diameter side.Further, this tapered driven roller 17₁₆ is in the taper size more than2.31×10⁻³ and its small diameter side is at this side in FIG. 61 and thelarge diameter side is at the inner part. Further, the roller surface ofthis tapered roller has been machined so that coefficient of staticfriction between the tapered driven roller 17₁₆ and the conveyor belt12₁₆ will become less than 0.26. Further, the compression springs18_(16A) and 18_(16B) have been adjusted so that a total applied load atthe this side and the inner side in the figure becomes more than 3 kg.On the other hand, the regulation belt 46₁₆ has been provided in oneunited body with the conveyor belt 12₁₆ at the large diameter side ofthe tapered driven roller 17₁₆.

The state of the conveyor belt 12₁₆ in this construction when operatedis as follows.

When the conveyor belt 12₁₆ is conveyed by the rotation of the beltdriving roller 16₁₆, the conveyor belt gradually moves toward the smalldiameter side of the tapered driven roller 17₁₆, that is, one-sided tothis side progressively by the tapered driven roller 17₁₆ and thecompression spring 18_(16B) with the applied load balance added. Whenthe conveyor belt 12₁₆ is one-sided progressively, the regulation belt46₁₆ provided at the inner part in the figure in a one united body withthe conveyor belt 12₁₆ contacts the large diameter side end of thetapered driven roller 17₁₆ and the conveyor belt is conveyed whileconstantly sliding. As the regulation belt 46₁₆ has been provided in oneunited body with the conveyor belt 12₁₆, if the one-sided movement ofthe conveyor belt 12₁₆ progresses by a certain amount, the regulationbelt 46₁₆ is balanced with the force at the large diameter side end ofthe tapered driven roller 17₁₆ and the one-sided movement is stopped.

On the other hand, as the zigzag running force of the conveyor belt 12₁₆is generally smaller than the one-sided moving force of the conveyorbelt 12₁₆, when it is balanced with the one-sided moving force, thezigzag running force is included in the action and the reaction of theone-sided moving force and no zigzag running of the conveyor belt istaken place. The zigzag and one-sided moving amount of the conveyor belt12₁₆ in the above construction were measured and the results are shownin FIG. 62.

That is, when the regulation belt 46₁₆ is constructed in one united bodywith the conveyor belt 12₁₆ and arranged at the large diameter side ofthe tapered driven roller 16₁₆ and the applied load balance of thecompression spring 18_(16B) at the large diameter side of this tapereddriven roller 17₁₆ is largely distributed, it becomes possible tocontrol the one-sided moving direction of the conveyor belt 12₁₆. As aresult, it become possible to control the progress of the one-sidedmoving and the zigzag running of the conveyor belt 12₁₆.

Further, when this tapered driven roller 17₁₆ is used, it is provided bytilting toward the driving roller 16₁₆ by 1/2 of the distance betweenthe diameters of the large diameter side and the small diameter sidethus the small diameter side of the conveyor belt 12₁₆ contacts to thephotosensitive drums. This is because if the rotating center axes of thedriving roller 16₁₆ and the tapered driven roller 17₁₆ are set parallelto each other, the small diameter side of the tapered driven roller 17₁₆does not contact the photosensitive drums, causing the impropertransfer. This state is shown in FIGS. 63A and 63B.

As explained above, when the taper size is selected at above 2.31×10⁻³,the conveyor belt 12₁₆ and the tapered driven roller 17₁₆ having thecoefficient of static friction 0.26 are used, the applied load at thelarge diameter side is increased by 10% more than that at the smalldiameter side and a load applied to the conveyor belt is set preferablyat above 3 kg, it becomes possible to control the one-sided movingdirection of the conveyor belt 12₁₆ so that it is one-sided stablytoward the small diameter side of the tapered driven roller 17₁₆.Further, when the regulation belt 46₁₆ is constructed in one united bodywith the conveyor belt 12₁₆ at the large diameter side of the tapereddriven roller 17₁₆, it becomes possible to suppress the one-sidedmovement and the zigzag running of the conveyor belt 12₁₆ simultaneouslywith high reliability.

What is claimed is:
 1. An image forming apparatus, comprising:means forforming an image on an image carrier means; a conveyor belt forconveying an image receiving medium to the image carrier means; means,having a first roller which has a diameter that is different at bothends and a taper size T expressed by T=(D-d)/L, wherein D is thediameter at the large diameter side, d is the diameter at the smalldiameter side and L is the length of the first roller, wherein T is morethan 2.31×10⁻³ and a coefficient of static friction is less than 0.26,and a second roller which is opposing to the first roller, for movingthe conveyor belt in a prescribed direction by rotating the first andthe second rollers in a state where the conveyor belt is put over thefirst and the second rollers; and means for transferring the imageformed on the image carrier means onto the image receiving medium.
 2. Animage forming apparatus as claimed in claim 1 further comprising aregulation member for regulating the one-sided movement of the conveyorbelt while sliding one end side of the conveyor belt that is positionedat the small diameter side of the first roller.
 3. An image formingapparatus as claimed in claim 1 further comprising a regulation guidemember provided in one united body with the edge side of the conveyorbelt positioned at the large diameter side of the first roller forregulating the one-sided movement of the conveyor belt while sliding onthe large diameter portion of the first roller when the conveyor belt isrunning.
 4. An image forming apparatus as claimed in claim 1, whereinthe image carrier means includes a plurality of image carriers and theconveyor belt sequentially conveys the image receiving medium to theplurality of image carriers.
 5. An image forming apparatus as claimed inclaim 1, wherein the first roller has a rotating shaft of which thelarge diameter side has been tilted by an angle θ shown by the followingexpression against the plane being parallel to the moving direction ofthe conveyor belt and including the rotating center shaft of the imagecarrier means:

    tan θ={(D-d)/2}/L.


6. An image forming apparatus as claimed in claim 1, wherein the Young'smodulus of the conveyor belt in the direction perpendicular to themoving direction of the conveyor belt is more than 200 kg/mm².
 7. Animage forming apparatus as claimed in claim 1, wherein the length (thebelt width) of the conveyor belt in the direction perpendicular to themoving direction of the belt is more than 50 mm.
 8. An image formingapparatus, comprising:means for forming an image on an image carriermeans; a conveyor belt for conveying an image receiving medium to theimage carrier means; means, having a first roller which has a diameterthat is different at both ends and a taper size T expressed byT=(D-d)/L, wherein D is the diameter at the large diameter side, d isthe diameter at the small diameter side and L is the length of the firstroller, wherein T is more than 2.31×10⁻³ and a coefficient of staticfriction is less than 0.26, and a second roller which is opposing to thefirst roller, for moving the conveyor belt in a prescribed direction byrotating the first and the second rollers in a state where the conveyorbelt is put over the first and the second rollers; means for applying aload set at more than 3 kg to the conveyor belt; and means fortransferring the image formed on the image carrier means onto the imagereceiving medium.
 9. An image forming apparatus, comprising:means forforming an image on an image carrier means; a conveyor belt forconveying an image receiving medium to the image carrier means; means,having a first roller which has a diameter that is different at bothends and a taper size T expressed by T=(D-d)/L, wherein D is thediameter at the large diameter side, d is the diameter at the smalldiameter side and L is the length of the first roller, wherein T is morethan 2.31×10⁻³ and a coefficient of static friction is less than 0.26,and a second roller which is opposing to the first roller, for movingthe conveyor belt in a prescribed direction by rotating the first andthe second rollers in a state where the conveyor belt is put over thefirst and the second rollers; means for transferring the image formed onthe image carrier means onto the image receiving medium; and a first anda second tension applying means for applying a tension to the conveyorbelt by giving a force to the small diameter side and the large diameterside of the first roller, wherein the force given to the small diameterside is smaller than the force given to the larger diameter side.
 10. Animage forming apparatus as claimed in claim 9, wherein a differencebetween the tensile forces given by the first and the second tensionapplying means is a value obtained from the following expression:

    {(Pa-Pb)/Pb}×100≧10

(where, Pa is a size of load applied by the first tension applyingmeans, Pb is a size of load applied by the second tension applyingmeans, wherein Pa>Pb).
 11. A conveying apparatus, comprising:a conveyorbelt for conveying an image receiving medium on which an image, which istransferred from an image carrier, is carried to the image carrier; andmeans, having a first roller which has a diameter that is different atboth ends and a taper size T expressed by T=(D-d)/L, wherein D is thediameter at the large diameter side, d is the diameter at the smalldiameter side and L is the length of the first roller, wherein T is morethan 2.31×10⁻³ and a coefficient of static friction is less than 0.26,and a second roller which is opposing to the first roller, for movingthe conveyor belt in a prescribed direction by rotating the first andthe second rollers in a state where the conveyor belt is put over thefirst and the second rollers.
 12. A conveying apparatus as claimed inclaim 11, wherein the first roller has a rotating shaft of which thelarge diameter side has been tilted by an angle θ shown by the followingexpression against the plane being parallel to the moving direction ofthe conveyor belt and including the rotating center shaft of the imagecarrier:

    tan θ={(D-d)/2}/L.


13. 13. A conveying apparatus as claimed in claim 11, wherein theYoung's modulus of the conveyor belt in the direction perpendicular tothe moving direction of the conveyor belt is more than 200 kg/mm².
 14. Aconveying apparatus as claimed in claim 11, wherein the length (the beltwidth) of the conveyor belt in the direction perpendicular to the movingdirection of the belt is more than 50 mm.
 15. A conveying apparatus asclaimed in claim 11 further comprising means for applying a load set atmore than 3 kg to the conveyor belt.
 16. A conveying apparatus asclaimed in claim 15 further comprising a first tension applying meansfor applying a tension to the conveyor belt by giving a force to thelarge diameter side of the first roller and a second tension applyingmeans for applying a tension to the conveyor belt by giving a force tothe small diameter side of the first roller, wherein the force of thefirst applying means is larger than that of the second applying means.17. A conveying apparatus as claimed in claim 11 further comprising aregulation member for regulating the one-sided movement of the conveyorbelt while sliding one end side of the conveyor belt that is positionedat the small diameter side of the first roller.
 18. A conveyingapparatus as claimed in claim 11 further comprising a regulation guidemember provided in one united body with the edge side of the conveyorbelt positioned at the large diameter side of the first roller forregulating the one-sided movement of the conveyor belt while sliding onthe large diameter portion of the first roller when the conveyor belt isrunning.
 19. An image forming apparatus, comprising:means for forming animage on an image carrier; a conveyor belt for conveying an image formedon the image carrier; and means, having a first roller which has adiameter that is different at both ends and a taper size T expressed byT=(D-d)/L, wherein D is the diameter at the large diameter side, d isthe diameter at the small diameter side and L is the length of the firstroller, wherein T is more than 2.31×10⁻³ and a coefficient of staticfriction is less than 0.26, and a second roller which is opposing to thefirst roller, for moving the conveyor belt in a prescribed direction byrotating the first and the second rollers in a state where the conveyorbelt is put over the first and the second rollers.
 20. A conveyingapparatus, comprising:a conveyor belt for conveying an image formed onan image carrier; and means, having a first roller which has a diameterthat is different at both ends and a taper size T expressed byT=(D-d)/L, wherein D is the diameter at the large diameter side, d isthe diameter at the small diameter side and L is the length of the firstroller, wherein T is more than 2.31×10⁻³ and a coefficient of staticfriction is less than 0.26, and a second roller which is opposing to thefirst roller, for moving the conveyor belt in a prescribed direction byrotating the first and the second rollers in a state where the conveyorbelt is put over the first and the second rollers.